Regardless of caliber this is good advice...practice, practice, practice.
Our PH told horror stories of clients showing up having never shot the gun they brought and the scope was only bore-sighted.
And to top it off they were usually .40 caliber or better...hello flinch.
Personally I have a 375H&H that I shoot comfortably and will be using it on a Cape Buffalo hunt.
Is this ideal...no.
Would I be better with a rimless 400 caliber for a DG hunt...absolutely.
However, I have very little experience with the 400's and as such will be sticking with my little 375.
I'll save the cost of a new rifle and spend it on practice ammo, range time and probably another Safari animal as well.
I will be comfortable and confident with my rifle, scope (with QD mounts) and open sights for the hunt.
"A man's got to know his limitations" Dirty Harry
Gotcha Harry, I know mine.