I have not tried any of those powders either, but hodgdon has load data listed for the 375 H&H 300 gr swft frames using 4451. Since the 375 Wby is just and improved 375 H&H, you can use a mid range load of the 375 H&H data, and use that for your 375 Wby starting load, and work up slowly. Or you can call Hodgdon. I tried IMR 4831 and H450, accurate but didn't get full speed.
Rob