AA4350...IMR4350...AA3100...IMR4831...
Although it's a Magnum cartridge and You're going to be pushing a heavy bullet, I'd focus more on powders in the Burn Rate Range of the 4 I've stated above. Although slower-than-stated powders offer some advantages, I've read alot of reviews/insight/feedback on powders slower than that, not producing the best accuracy...some of those super-slow powders are just a little too Dad-Gum slow...
It's .308" caliber, not .264" or .257" or the like. I'd invest in powders of the burn rate range that's been stated the most, so far on this post/thread, before trying a powder slower than the AA3100/IMR4831 burn rate.
Even my .270 Winchester prefers powders of the 4350 relative burn rate over slower powders, and still, I'm going to be looking into other faster powders as soon as I can, such as AA2700 and IMR4064 for most of the bullet weight range in .277"/.270 Win. I
feel that powders slower than AA3100/IMR4831 are, in most of the common magnum cartridges, overrated/too slow, especially in .30 caliber.
If I were embarking on the endeavour that You are, I'd also try to gather a little info from BenchResters that shoot the same or similar cartridge. AND, as already stated, consult as much Published Load Data as possible.