I think you are on the right track. H1000 is my current favorite in my .300 Win Mag but 7828 and Retumbo would be my next two choices. Especially with the heavier bullets Retumbo might get a bit more velocity.
I know a lot of guys love RL22 in that caliber and I have shot a bit of it but haven't had the best luck with it personally. Also, like you mention, RL22 is very temperature sensitive if that bothers you but honestly it usually isn't an issue unless shooting really far in extreme temperatures.
If you were running a little lighter bullets I really like IMR 4350.
Good luck
