I know a lot of guys have great luck with RL-22 and the 180 AB. A buddy of mine shoots 75gr. (I think) of RL-22 and 180 AB out of his 300 WM. He is really happy with it. Two elk, and a nice buck are not so happy with it.
My brother in-law shoots Retumbo with the 185 Berger with great results. I know Retumbo is slower than RL-25, but I don't think he is getting any better speeds than the guys that use RL-22. If I remember right, the Retumbo load that he settled on is going right at 3000 fps, and is compressed.
Tried RL25 with 200 PT's awhile back and it didn't seem to be as easy to get the speed and accuracy I get with RL22. Probably just my rifle, as RL25 works well in some of my rifles, but RL22 is king for the 300 Win Mag in my eyes.
I haven't shot a 300 Win Mag for about 20 years. RL25 wasn't even around then.
My go to load in that particular rifle was 82 grs of H1000.
I think I'll start with RL22