The "Big Eight" - Really?
IMO that's the wrong powder to get max velocities out of anything heavier than the 150gr (maybe as high as the 180gr).
I don't have a 325 WSM or even a pipsqueak 8mm Rem Mag. My 8mm ARP is based on the 338 RUM and holds about 10% more powder than the 8mm Rem Mag. For the heavier bullets, it works best with powders in the RL22/H1000 to RL25/Retumbo+ range, pushing 180's at 3450, 200's at 3225 and 220's at 3170 fps (with 104.0 grs of US869). If you get within 50-100 fps of those numbers with an 8mm Rem Mag, you're way over the pressure red line.