Depends on your perspective, LD. Personally, like the poster above, I believe the way to improve the 375 H&H is go to a bigger bullet. For animals typically hunted with the 375 bores, it isn't an extreme long distance affair. Not the way the 30 calibers are used. The H&H version shoots plenty fast enough to have MPBR for the way animals are hunted using the 375's. To improve the "killing" ability of H&H, I believe, it is better to go up in caliber size than case size. The H&H is fast enough to provide all the gained effects of a high velocity round, both in trajectory and shock value.
By the way, though the Weatherby version of the 300 does add some velocity to the H&H version, when loaded to the same pressures, the velocity gain hardly exceeds 75-100 fps, especially when using the 180 and 200 grain bullets.