I have slimmer legs and the attacks are my go to pant. I have the guide pants as well but rarely wear them because they are so loose in the thighs so they may be just right for you.
I am currently in the load development process for a 7 PRC +P. I started with the 180gr ELD-M but it was not grouping that great so I switched to the 180 berger hybrid target and it has been much more consistent. Seems to like either 15-20 thou off or 80-100 thou off.
I agree with the other responses as far as 6.5 SAUM being a bad choice if you are not reloading. The 6.5 PRC with a SAMMI chamber is a very capable cartridge on its own. I would consider having one rifle and two different loads. A lighter factory load with a 140 class bullet and hotter load...