What kind of accuracy are you getting with the WW760? I was pretty impressed by the accuracy exhibited by the .375 WBY w/H414.
I normally test velocity and accuracy separately, so the Magnetospeed hanging on the barrel doesn't present a problem for me. Portability and versatility are the selling points for me. Don't know whether CFE would cause an issue or not. I was trying that with 250g TTSX's in my H&H, but never finished development. It would be interesting to see if an issue arises with that or not.
I haven't tried the Speer bullet. I have some Hornady 270g SP flat base bullets that I will probably never shoot. Alliant shows data with the Speer BTSP in H&H. It should get you in the ballpark for a starting load:
Alliant Powder - Reloader's Guide
Hodgdon shows .375 Ruger data for the above mentioned Hornady bullet. Again, not exact, but should get you in the ballpark:
Cartridge Loads - Hodgdon Reloading Data Center - data.hodgdon.com