Retumbo is a little slow. I've tried it, I didn't get great accuracy, but I am only working with one bullet. You might have better luck.
I've heard people like H1000 in 7wsm on other forums, and that is what I would like to try next.
Otherwise, RL22, H4831, IMR7828, RL17, or Magpro would be some more to look at. Alliant has some new power pro powders listed that promise good velocity.
Definitely use the magnum primer for spherical powders. Not a bad idea in any case.
My best load for accuracy was 140 triple shocks and H4350. That was a good load, but I want to use higher bc bullets in the wsm and us my 30-06 for shorter range hunting.