The macabre facts of combat are that the outcome usually requires a death or disability. This is of course outside the scope of our reenactment combat. However, knowing the realities can help us in our theatrical portrayal. It also makes good conversation with members of the public; especially the squeamish ones.
Human beings are by nature very hard to kill or disable (except when they aren't). By very design we are extremely durable with many redundant systems that can prove surprisingly resilient. Although death may be the end result of many injuries; even horrific wounds can see an individual last a very long time. To kill or disable an opponent with an edged weapon you have a choice between damaging the mechanicals or the hydraulics. To damage the mechanicals you need to cut nerves, ligaments, muscles and tendons, break bones and joints. It also helps if you rattle the brain around. The hydraulics are damaged by making holes in the largest blood vessels or a large number of small ones. Blade weapons can deal this damage in either a thrust or cut. Where the cut is better for mechanical damage; the thrust is indeed better for upsetting the hydrodynamics of the opponent. Both are capable of causing death by later infection but this is innefficient by duelling standards. It is ironic that a fatal thrust through the body will often result in a more dangerous opponent; for a short period of time, and yet a cut can render them ineffective, without necessarily causing death. This point is mentioned several times in the works of George Silver from the early 17th century.
Most exponents of civilian weapon combat were overly fond of the thrust attack. De Grassi mentions, in his arguments, the fact that Romans used the thrust to great effect. This is of course true but a quick examination of the gladius and pugio (dagger) shows that these thrusting weapons are gifted with rather broad dimensions unlike the civilian weapons of the 16-17th centuries. Being stabbed in the stomach with a pugio would be rather like being disembowelled with a small shovel. A stab from a gladius would be similarly horrific. Of course we can wonder if the Italian 5 finger dagger (Cinqueda) of the Renaissance period wasn't a rediscovery of this fact.
If a slim weapon transfixes the human body there are in fact few areas which will guarantee rapid death. It would be analogous to think of a single shot from a small calibre firearm. A powerful (and lucky) swordsman with a sturdy blade may just be able to stab into the skull and damage the brain. In fact Capoferro shows several "through the head" thrusts; all of which I think are quite fanciful. The skull is extremely strong, especially in living people, and trying to ram a sword through would more likely result in a superficial cut, a lot of bloody and an hysterical opponent. Of course, some may argue that a thrust through the eye socket, nose or mouth will guide the blade through a thinner piece of skull and "viola". Good luck to you I say; rather like trying to shoot a bird in flight. The bone behind the eye and part of the nose is in fact thinner. Thrusting up through the palate is unlikely (it's not thin at all), although you might be lucky enough to go through the neck and take out something important.
The neck is in fact an excellent target for the thrust and most wounds should prove to be rapidly fatal; especially if the weapon is not drawn straight back but rather twisted or ripped sideways. However, thrusting through the neck in the full throes of combat would require a great deal of skill and an equal portion of luck. Since the thrust is a linear attack it is easy to dodge or ward and the "target area" in this case is fairly small. Also people don't like things being poked at the throat and are very good at putting other things (like hands) in the way. It is not uncommon for stabbing victims to have cuts all over the hands and forearms from warding blows.
One would imagine the heart is an excellent target for a thrust; and a dead cert for a kill too but... In fact the ribs are excellent protection and you are unlikely to thrust though a rib bone. Of course you could thrust between the ribs. This would mean rolling the sword over to present horizontal to the chest. In this case you would have less than a 50% chance of going between the ribs and then into the chest. Then all you have to do is find the heart or one of the main blood vessels at least. This of course is pretty hard to do. Even if you managed to penetrate the chest the more likely outcome is a mortally wounded opponent who will insist on taking you along for the ride. I have seen some glorious forensic pictures of stabbing victims and the amazing thing is the number of glancing wounds to the chests and the horrific tears in the abdominal wall.
Stabbing up and under the ribs is pretty hard to with a sword unless your opponent is prone, on horseback, or you are a dwarf. This is of course easier to do with a dagger. The way to a mans heart is of course though his stomach. On the other side you will need to nick the liver en-passant so to speak. The great descending aorta which runs down the back of the abdominal wall is also an excellent target for a quick kill and death will occur in seconds if you can nick this large and highly pressurised artery. The problem is that it is very deep with lots of squishy stuff in front that will get messy at the passing of an edged weapon. The stomach muscles tend to bunch and writhe when they are cut so it is hard to stay on target too. I am also told that a forceful penetration of the stomach is accompanied by a rather distracting "popping" noise which might also spoil your aim; the first time anyway.
As the descending aorta branches to divert blood out to the kidneys and then the legs we are still able to kill swiftly if we can cut the blood vessels at this level. A thrust to the groin or back (just under the last ribs) might also take out a large vessel. The femoral (groin) and renal (kidney) arteries are fairly big but still not huge targets. Imagine trying to thrust at a piece of 3/4 inch rope swinging in mid air. The rope would be is easier to hit than these large arteries. Also the piece of rope isn't trying to put 3 feet of steel into you as well.
Other large blood vessels in the upper arm, armpit, behind the knee, thigh etc are all good targets for thrusts but don't count on a rapid death. It's the same with large organs like the kidney, spleen, lungs etc. Although they do have large blood vessels and lots of little ones; wounds are unlikely to lose blood fast enough for the quick death. Most adult males need to lose at least 1 litre of blood before shock sets in let alone unconsciousness. Adrenalin and sheer bloody mindedness can be counted on the keep an opponent functioning long enough to do some damage; unless you can run faster than them.
That a cut is much slower than a thrust can be argued to hell and back. Of course a lighter weapon can be moved faster but in a cut or a thrust invariably the hand is moved through the same distance and so the execution is similar in time for each manoeuvre. Also one must point out that since most combat begins with opponents a step or so out of range with each other, the blow delivered can never be faster than the step into combat anyway. This is what George Silver calls the time of the foot. It might be worth noting here that most peoples reaction time (when a decision needs to be made) is rarely better than about half a second. A sword blow (cut or thrust) can often be delivered in well under half a second. If two opponents are already in range of each other, then the first to deliver a blow will most likely succeed. Mr Silver makes reference to this in saying that the hand is quicker than the eye. This is pretty obvious when you think about it; just look at Olympic fencing.
As the reader might imagine this text has been a very abridged version of cut and thrust injury. Should I have chosen to write a truly authoritative work you can rest assured the size would have been enormous. For those who may be wondering, my information is compiled from my training in anatomy, anecdotes from my hospital work environment, discussions with doctors experienced in trauma, and lots of reading. Since my own experiences in penetrating wounds is limited, you can take it as read that my conclusions are, for the most part, second hand (thank god).