I have used all of the following doubles in Africa and North America.

I have taken NA game,plains game, cape buff and elephant with all 3.

My 450 No2 is my favorite rifle of all time.

I think the 450/400 [mine is a 3 1/4"] is the best choice in a double for all round use for the modern Safari hunter.
ESPECIALLY if scoped.

My 9,3x74R Chapuis Double, scoped of course, is my favorite hunting rifle under 40 cal.

While I believe in Physics, I must report that in actual use I have not been able to tell any difference in effectiveness between the calibres.

I will admit I feel a little better with the 450 or the 400 when around elephants, but I know if I hit them right with the 9,3 all will be well.

I would prefer the 9,3 double to any bolt rifle for African DG.