I have the F1 tall mainframe and it fits great (I’m 6’2”). The adjustability that the frame provides really makes it easy to adjust and fit to any preference and feel. I have gone through a few iterations of bags and pouches on the frame and now run two hip pouches and a water bottle holster...
I had a Predator in 6.5 creedmoor a few years and noticed the same thing. My barrel would regularly have higher velocities than published in loading manuals. It ended up staying consistent through the life of the barrel.