I don't know as there is a plains game animal that could take a 270 grains Barnes TSX at 2700 fps in a vital zone and not crumple up within a hundred yards. In fact I wouldn't hesitate to use it on buffalo if a good shot presented itself. While I don't own a .375 Ruger, I do have a .375 H&H which is a slighlty less volumous case. My load with the 270 grain is 77 grains Alliant Reloder 17. It averages 2650 in my rifle and is low pressure. That would likely be a good starting point for a .375 Ruger. Max load was over 80 grains for the H&H if I remember correctly. It also shoots within 1.5 MOA. That's much better than I can shoot it off hand. I know the round is going to hit within .75MOA of where I put the crosshairs. Thats +/- 2.25" at 300 yards. Thats good enough to hit woodchucks with! So Maybe you don't want to take load advice from me because I don't strain to get a 1.5" group down to .75" at 100 yards because all the burned powder and wasted bullets are not worth it to me. I like to prectice and not shoot off a bench anyway. If I were shooting at 600 yards, things would be different.
So, take it for what it's worth, I think Reloder 17 is THE powder for .375. Even if you give up a couple tenths of a MOA, The powder is incredibly efficient and 2800 fps with a 270 is easily possible with the .375 H&H. With the Ruger, you'd get even more. Just my $.02