I have a Tikka T3 stainless in 300WSM and want to load 165 Hornady SST. The 2 powders I have are Varget and IMR-4350. I like the idea of Varget because of the temperature stability but the Hornady people don't recommend it, even though it is listed in numerous reloading manuals.
I have the same rifle ... good choice! I primarily shoot the 180 gr AB's in mine and I like H4350 for mine. If memory serves, I use varget for 110 gr vmax's out of it. IMR and H are very close to eachother and the H is much more temp stable than IMR. Reloader 17 would be another option, it is also very close to the IMR and H 4350. Standard LRprimers is all you need in the wsm.
I used to re-load but now I "hand-load".
-- Well, at least I try --
So far I've shot RL-19, Varget, and H4381sc through my plain jane Weatherby Vanguard with 150 gr Hornady SST. All three were acceptably accurate for 200yard shooting but Varget won hands down in accuracy. I got MOA accuracy with Varget. I haven't done anything to 'accurize' my weatherby either.