Sorry I was too quick too answer all proper manufactured sporting rifles is bascially a M98 or copy.
Lee actions were never adopted much by the classic gunsmith for building sporting rifles.
Emm, I have & had a LOT of nice Classic Sporting rifles from H&H, WR, C&H, Fraser, Greener & many others in .303 Brit from Farquharson Falling Block, Martini Drop Block, Enfield/Lee Bolts (still have lots of Lee Speed/BSAs) Mauser Bolts, even Double Rifles & Cape Guns, I still have a lovely Westley Richards in 400/360NE that is a rebored .303 Brit.
I believe the question is which is more "Classic" not most useful or what "you" would like to use ?
Then I would differently say the .303 Brit !
I dare say that the .303 Brit was chambered in more rifles by more manufacturers in a greater configuration of firearms than the .275, especially in "Classic" times ?
I most likely would use it over a .275-7x57 but wouldn't say it was that much better as I don't think it is as a caliber choice, would most likely carry a .375H&H of some type to cover it all, but I do love my .458Win Mag lol !
For soft recoil, light carry rifle, shooting support supply's/ I might well pick a 6.5x53R or 6.5X54 in Classic times ?
If we were just talking South Africa, which I don’t think we are ?
I don’t think even there the 7x57 was used much before or at all before the Boer War, I think an early Martini or even more a Monkeytail Westley Richards ?