70 grains looks like the sweet spot. I'll be honest, I didn't play around too much with the Bullshops in finding the powder sweet spot because he first time I shot them out of my 700ML I had a one hole group. That was with 80g 777 2f.
That load is more than stout enough for anything you'd be shooting. And at the distances you shoot you don't have to worry about drop.
Granted I've only shot one elk with the 460 Bullshops but I was more than impressed. Anytime you can boom-flop an elk I think you've got a good combo.