Belts on a cartridge case are superfluous, they had their purpose but are generally useless for modern cartridges.  As much as the 7mmRM is a personal favorite, a beltless version would be my preference.  The 300 WM could use an updating as well, remove the belt, lengthen the neck and clean up the shoulder.  I do like new and improved but I'm also not against things that work.  If 7mm PRC ammo became readily available, I'd build one tomorrow but I'll wait for the ammo to show up on retail shelves.  On the other hand, I've tried most of the 6.5s and I'll keep my 270 Win as it was designed right from the start.  I do prefer my shots on game to be under 300 yards, under 200 even better, but that doesn't mean that I don't like accurate rifles and well designed cartridge cases.