I have to disagree with Category C.
Category C - Are you a competition shooter blasting away looking for your next gold medal?
These shooters should be looking into rifles that fit into the Governments Technical Data Package (TDP), often referred to as Mil-Spec standards.
Because a high power competition shooter does not want a M4 type Mil-spec rifle.
They don't want a 16" chrome lined bore, they want a 20-24" match grade hand honed stainless target barrel. They don't want a 6 position M4 stock, they want an A2 stock, they don't want double heat shield hand guards they want a CMP legal free float tube. They don't want a mil-spec trigger they want a Giessel. They don't want mil-spec sights they want target sights.
Matter of fact the only milspec or TDP parts a serious target shooter might want to use is the bolt and extractor.
I don't see many 3-gun competitors shooting Mil-Spec guns either, they are generally much more customized.
If you are a competitor you need a gun tailored to your specific competition needs, not the military's needs.
I would change Category C to a high volume shooter instead of competitor. There are folks out there that like to shoot their rifles a lot, take multi day training classes several times a year, and generally burn through 5K rounds or more a year in their rifles.
Actually to keep some from getting but hurt or insulted by your descriptions I would change A to a low volume shooter, like you mentioned 200-300 rounds a year. Change B to a medium volume shooter, ie 200-300 rounds a month or 2,000-3,000 rounds a year.
I also don't know where you are getting $100 difference between those that meet the TDP (ie Colt or BCM) and the next lower level of guns.
A Bravo Company M4 Mod1 is $1,135 from Bravo Company. Colt 6920 is about the same price.
S+W's, Rock Rivers, Bushmaster, and many others with similar features (features like removable carrying handle, spare mag, sling, ect...) are retailing around $800 right now. That's over a $300 difference. And before someone mentions buying the upper and lower separately from BCM, if I do the same with other mid tier brands I can get their prices down cheaper too.
Now if you are counting on a gun to save your life I really don't think $300 should be the driving factor. But it is quite a bit more then the $100 you claim.