As stated—if you reload, and the price is right, you can load it down in FPS and match the HH.
If you can handle the Weatherby configurations [stock]. And the price is right.
You can always load down but not always up. So if the price is —you get the message.
Never makes sense to try and make something it is not...just because the price seems right, wrong way to go about it.
Loading it down is not always the right way to go especially if you plan on using heavy for caliber bullets. The twist rate of the barrel is wrong and you will have issues with bullet stabilization.
Now you have a push feed action rifle, with the wrong barrel twist, with an excessively long barrel, probably fitted with a muzzle brake, that has no "iron"/open sights, that needs brass that is very hard to come by and expensive and it only takes two in the magazine, what for???
So you can say, I have a 378 Weatherby that I download to 375 H&H velocity but it aint as great as what I thought?
No No No sir, let common sense prevail, pass on this deal and buy yourself a proper hunting rifle in any number of calibers you prefer, but not a 378 Weatherby.
Make an arrangement to go and shoot this rifle, one shot will make the decision for you.
Good luck.
PS. Make sure you dont creep the stock.
