Had to think about which of my guns I like best and maybe more important use the most. First off I will be the first to admit I have a double rifle addiction, and will say that I have more double guns then I can really justify and what is worse always thinking of adding another.

Calibers currently include 303 British, 9.3x74R, 375 FM, 375R V-C, 450-400, 450 BPS, 450 Nitro, 45-70, 500 Nitro, 577 Nitro (also have two rifled SXS shotguns a 12 and a 20). I keep thinking about the 30R Blaser, and maybe even something smaller....6.5x57R or maybe the old 22 Savage but so far I am able to take a cold shower and the "need" will temp go away.

The calibers I reach for most often are the 303, 375FM, 375R V-C, 450-400, and the 450 Nitro. Two of the guns are two barrel sets. The 303 and 375 FM is one gun, the 375R V-C and 450 Nitro is the other.
And the one gun I have that I use the most is the 303, it is more than adequate for most of what I do in the lower 48 states.

If you have to rely only on factory ammo and want a gun only for Europe (driven game) I would probably look closely at the 8x57jrs, plenty of power for European game, easy to find ammo, very mild recoil for a fast second shot. Although I currently do own a gun in that caliber I have used it on driven pigs in France and moose (elg/elk) in Sweden and they all went down quickly and I never felt under gunned. My second choice would be the 9.3x74R, more recoil so a slightly slower second shot.

If you reload, and thinking about the 9.3 then the 375FM deserves a hard look. Does all the 9.3 does and then some. I also feel it recoils less, probably because the larger case and lower pressure.
Also the 375FM guns will probably be heavier. Many of the 9.3's you see are very light, with many under 7lb. I almost never shoot or hunt with my 9.3 anymore, the more I use the 375 FM the better I like it.