The 6.5 PRC started the PRC trend. Fellow was looking for a cartridge for comp shooting. It a good read , I would suggest googling it.
As others have said a 300prc is a revamped 300wm. It is intended for the higher BC bullets as all of the PRC cartridges are to capitalize on the long range hunting trend thats going on.
I have a few 300wm and can stretch them out past 1000 yards and I do it quite often when the weather is nice. But personally I will not take a shot much past 500 yards if that far on live game. To much can go wrong, miscalculation on range, wind etc. The time of flight it takes for the bullet to impact, if the animal moves I could go on. Each to there own for long range hunting. Target shooting I love shooting way out there, I do not like shooting way out there then having to go look for a wounded animals blood trail.
That being said my next rifle will probably be a 6.5prc. Ease of recoil and High BC. Plus its a fine round for antelope on up to supposedly elk, I would still use my 30cal or 375 for elk though.