In my experience, every powder that was suggested to me, ended up being a bit slow for the 6.5 PRC. I tried H1000, Retumbo, N565, etc. Once I moved to running N560, the groups/SD's really tightened up. Playing around with GRT, N560 will give you 100% burn with a 22" barrel or longer and roughly 97% case fill. For comparison, N565 will be a compressed load before you can get complete burn and require roughly a 23" barrel. If you are going to be running a 20" barrel, I would suggest even looking at N555. N555 in my rifle gave me some of my best groups but does come up a little short on velocity compared to the other powders. It's going to depend on your specific rifle. You have your projectile selected so grab 3-5 different powders, load 10 shot ladder tests in .3 grain increments, shoot them and see which powder gives you the smallest group across the ladder test. That will tell you which powder is going to be best for your rifle. If you don't have Gordons Reloading Tool, hit me with your rifle specifics and I can get you exact numbers and suggestions.