I'm using IMR 4350 powder with my 300 RUM and 200 grain Accubonds but, only getting a chronographed muzzle velocity of 2940 , with less than .5" three shot groups. I have had several groups at 1/4", which tells me the rifle and load are more accurate than I am. I've seen reports that guys using Rotumbo powder are getting the kinds of muzzle velocities you mentioned. In real life hunting scenarios I don't think there is really any practical difference in a couple hundred fps in muzzle velocity, so I stay with my extremely accurate load. Not to say that I wouldn't be as accurate with another powder, but I use IMR 4350 with great success in several of my rifle calibers. One less powder, I need to keep on hand. Just for your info my load uses 77 grains of IMR 4350 with Fed 215 mag primers. Nosler calls out the powder range of 77 grains min to 81 grains max.
Good luck finding your load. I enjoy the load development work.
