I don't understand why because its name the 275 Rigby must go to a Rigby (Mauser) rifle and a 30-06, because the same reason, to a G&H or Springfield...
Since almost their origins, the Sporting Mausers were chambered for the 30-06 and, since around 1924, also the Mannlicher-Schoenauer. The same with the 9,3x62. Of course, also the 7x57/.275 Rigby (Rigby, at WDM Bell and Jim Corbett times, named their rifles 7mm Mauser, not .275 Rigby...). By the way, the 7x57 was chambered, also from the early XX Century, in all the made in USA rifles!
So, as I see, any of these three cartridges matches a Rigby rifle perfectly!
And as a user of all, I would be happy with any of them. My choice would be dictacted mainly by the hunts proyected.
Best!
CF