tadge; I like James' idea of the Savage and switching barrels. From what I've seen of the buffalo down there (movies and TV), a 7 Mag or a .30 mag would not be my choice for them. A .338 Win mag would be O.K., a .340 Wby good, .338 Rum better and a .375 H&H or .416 Rem Mag about right. Problem with the bigger calibers is their recoil and the cost of ammo. Prone shooting will get objectional quickly unless you can manage a 15 - 18 lb rifle, and I don't know if there is a weight limit on F-class, but I think that muzzle brakes may not be allowed. On the other hand, I killed a 400 lb feral boar with a heart shot from a 7-08, so I wouldn't hesitate to hunt them with a 7 Rem Mag. It is also an excellent 1000 yd target caliber, recoil is mild, and hunting ammo is not too expensive. The long range ammo will have to be handloads.
The ideal solution is 2 rifles. Barring that, I don't see one cartridge being suitable for both jobs, so a Savage switch barrel setup is an option worth looking at. Biggest drawback I see is the need to re-zero at each barrel change, or use 2 scopes and just check zero each time you switch barrels. A good long range scope is not going to be a good scope for dangerous game hunting.
Remember that these are just my opinions. I will watch this thread and look forward to seeing what ideas and solutions are offered.
Best of luck, Tom
Texas State Rifle Association Life Member
NRA Endowment Life Member
A big fast bullet will beat a little fast bullet every time