I can't speak for the straight walled cases, but in my 500/450 3-1/2" magnum BPE double rifle I'm running 76 grains of Varget topped with 21 grains of dacron wadding behind a Hornady 350gr SNRN for ~2025fpsMV

Wright has a similar load in his book, including pressure data -- but that's a bottleneck case, not a straight walled case.

This load runs consistently in my rifle.
Have you considered bottleneck cases?
I use 450no2NE brass, this load is easy on the brass with no stretch to speak of - I neck size only and reload...

Cheers
Tinker