BigMike,

Sounds like you have found the right combination. Congrats.

If everything from 300-425 regulates @ 1770 fps then you've got a "keeper".

FWIW, I killed my American Buffalo (Bison) with a 45/70 loaded w/405grs @ 1800fps. Dead, dead

So I'd try the 425's and see which shoots the best....hard to go wrong with the results you are getting with the 400's.