You can get that 100FPS difference by handloads if speed is your thing. You can get a flatter trajectory by using copper bullets that have more volume at a given mass.
So then it comes down to the gun itself. Many 375 weatherby rifles are indeed, weatherby rifles. Most credible 375HH rifles for Africa are controlled round feed, nearly all Weatherby rifles ever made (excluding early mausers) are push feed.
So if you decide you're going to get a CRF rifle and are eyeing the 375 weatherby, the question then becomes why would you spend all that custom money to accomplish about what a 375HH will do? Might was well get a 404J or another caliber where the juice is worth the squeeze of paying all that expense for a CRF custom.
Just my thoughts. I've never missed an animal or failed to kill cleanly due to a missing 100fps, but I sure have had issues with bad stock fit, jams, and failure to extract. For those reasons I don't want a weatherby branded gun, I want a foolproof CRF in a very reliable caliber for extraction like 375HH, 404J, 458WM, 416 Rigby, etc.