I hope you don't mind me jumping in, but I'll take A4s request for some Marine feedback. During my limited time in the Corps, I have learned a new respect for the M16A2. It is a reliable weapon as long as you keep it clean, and it has very good accuracy even at long range. Some problems with the feed system were fixed with the addition of the forward assist which enables a semi-fed round to be forced into the chamber. From my buddies who have been to Iraq/Afghanistan/Haiti, and from senior enlisted who were in Desert Storm/Somalia, there seems to be an agreement that the 5.56 round doesn't have the stopping power needed. Many have fired multiple chest shots in order to bring down a single target. The M4 does lack the range of an M16, but this is rarely a factor. AK47 is a good weapon- it is very reliable (I'm sure everyone has heard the stories of those that were found buried in sand and then still able to shoot). The stopping power of the 7.62x39mm is much better than the 5.56. The AK47 definitely does not have the effective range or accuracy of the M16 though. The effective range is 400 meters, but that is a questionable number if you have ever fired one. The Marines, as you may know, qualify out to 500 yds, and 600 and 800 yards is possible with a well trained shooter.
Final word- everything I have heard about the new M16A4 being issued is good (I have yet to fire one though).
Just my two cents.