H1000 won't get you great results. You won't be able to get enough in the case for maximum performance.
IMR 7828ssc is my new favorite powder in the 300 WSM
. It is about as good as I have found for the slow burners and the ES in my loads have been fantastic. I worked up a 210 Berger load with 7828ssc last week and I had six straight duplicating velocities with one particular powder charge. I thought maybe the chrono was spewing some foolishness until I went to the next powder charge and started getting very close but different velocity readings for each shot again. I have found 7828 to be insensitive to temps ranging from 25* to 80* in loads using the 210 VLD and the 230 Tactical.
I like 4831sc for the 200+ bullets too, but the speeds on 7828ssc have been a bit better. I use a standard CCI 200 in Norma brass for all my 300 WSM loads now.
I have worked up some good loads with RL17 and the 200 Accubond as well, but they got a bit squirrely in hot temps. Great hunting round though.
Great choice on going with the heavies in the 300 WSM, they really sing with the high BC bullets.