My current .375 H&H has a Leupold 2.5x8 sitting on it, and it seems to be a very nice power range. Previously I had a Leupold 1.5x5 on one, but rarely fired at game with the lowest power setting (although I always carried it that way). The higher power is very useful for plains game, and the Leupolds are very rugged. The 2.5 power has worked well for me on cape buffalo, and if the brush/grass is extremely thick I can remove the scope. Recoil from a full power .375 load makes a guy appreciate long eye relief, and it is a scope killer. I see quite a few Swarovski scopes on .375 rifles, and they are great, but some guys like me would rather put the extra $1,500 into the hunt rather than the scope.
I would not scope any rifle larger than a .375.