What's the PSI dealt by a person of average build for basic punches and kicks?

What you are asking is impossible to say. There really has been no objective testing of these for a large enough cross section of the population in order to get average values. There have been some testing of different techniques. However these have all been small test using only a few experienced martial artists. Unless you could test hundreds of different people of various levels of skill from various styles, you will have very slanted results. My background includes Mechanical Engineering. In Science and Engineering a few results done on a small group of people would simply not be looked at as being reliable results. Much testing of many different people over a long time would be necessary for reliable information.

As for effectiveness a technique is not more effective simply because it is more powerful. Many powerful techniques fail to stop an attacker. An effective technique is any that accomplish stopping the attacker. It may or may not be very powerful.

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Fight Science had something on this a year or so back and from that and several articles that I have read most adult males can punch with the force of 100-180 pounds per square inch. A trained fighter though can punch with more force than that and that can easily range in the 250-350 pounds per square inch. The Fight Science show seemed to bare that out and they were using some pretty sophisticated instruments for measuring all this and had Chuck Liddell on and he could hit with a force well over that.

You might try to research this on the web and that particular episode. They also measured the force of some kicks and those were in the range of several hundred pounds and I believe they had Rampage Jackson for that.

There of course will be some variation with any of these though as a kick with the front leg or a punch with the front hand will always be weaker than a kick or punch with the rear hand. This is because you can not put your weight behind a lead hand punch or lead leg kick or transfer that weight forward slightly like you can with a rear hand punch or rear leg kick.

A lot of all this that I have read as well as seen is probably pretty accurate as far as the correlation between the average person and a trained fighter. Many of the guys that walk into the gym who are physically bigger and stronger than myself can not hit a heavy bag as hard. They lack the skill, technique and coordinated action of different muscles and their body performing this. However that does not stay that way and I can have most people punching about three times harder than they did when they first came in the door in a month or so.