Actualy I was funnin with you a little on the big bores. I couldn't respond earlier due to being at work all week.
BTW, I voted for the 416Rigby, but the 375H&H is also a good choice (375H&H is the minimum cartridge, in some countries, for hunting the "big 5"). The 375 has a better bullet selection and about 1/3 less recoil than the Rigby (if that matters to you).
High pressure and fairly streight cases may give problems in the heat with feeding/extraction (there's a reason the classics have such tapered cases and low pressures).
Just for grins, this thread contains some photo's of Ed Hubbles big bore wildcats and there parent cases http://forums.accuratereloading.com/...3502#605103502