6,5x55 is a good round, no doubt, but I think the 7,65x53 is a good one too. something between 308 Win and 8x57 its fine for any european game. If I ever stumble about a Mauser 91 for a good price it would be a big temtation.

why dont you look for an original 7,65 argentine barrel? I think it must be possible to find this because so many argentine rifle's are butchered for the action. I would ever take an original period barrel if possible. simply ask gunmaker who make custom mauser's they must have it.