Most comparisons between 7RM & 7PRC came to the conclusion that if you already have a 7RM, no need to get a 7PRC. If you are just starting out, they both are good choices, but if you want heavy commercial ammo, go with the PRC. You can do anything you want if you are getting a custom barrel with twist and throating, but if you have to pick up a box of ammo at the local LGS, the off the shelf 7RM ammo will be a disappointment. I love my 7 Sherman Short (and vibes with your less powder theme), but in a Long Action, it is a waste. I have no experience with the Mega or Max, but it seems they thrive in the Medium (XM) actions vs the Long. I think the LA and less powder with a Mag bolt face is an oxymoron. In short, with your setup and criteria, 7PRC.