.375 H&H over .375 Flanged, or for that matter .416 Rigby in a double

I've seen a good bit of cautionary advice saying don't buy a double in a cartridge without a rim, how much weight should I give this? I'm already set up for .375 H&H, brass is easily attainable, and a Krieghoff in the H&H would be a gem for me- if of course I'm not handicapping a magnificent rifle with a non-rimmed cartridge. .416 Rigby in a Merkel 140 also interests me, however a feel slightly better about the belted H&H over the rimless Rigby. Is this misguided or foolhardy? I would hunt...

.375 H&H over .375 Flanged, or for that matter .416 Rigby in a double