H1000 would be my first choice and then Retumbo. In my 300RUM, Retumbo has not proven to be a velocity advantage over H1000. The Retumbo shows pressure on the case quicker than H1000 too. This is my rifle though.
I have had very good experience with RL22 in in the 300 um. I did try VV n170 once, but the muzzle blast was wicked, and I mean WICKED. RL 22 is my usual go to powder in my 7RUM as well. The only thing about rl22 is that it is very temp sensitive, be careful when the temp rises. Good luck and good shooting. AIM SMALL, MISS SMALL