The 338x 74R sounds neat!!

A DR regulated for a 250 grain would have a SD of .313 and the Woodleigh 300 gr a SD of .375 and that should be plenty good for african plains game. The 250 gr should be great and would be the one a DR would presumably be regulated for!

In a pinch this wildcat may handle Buff as well!!

I am certainly not one to dtermine the need for a certain wildcat but it still sounds like a fun Double rifle unless I have missed something.