I love Sakos, particularly the 75 which I use most and would be hard pressed to part with under any circumstances. My two closest stalking companions both shoot 85's which are nearly as nice. The safety is quieter and more intuitive to me on a Sako but the safety system on the Mauser seems, well, safer. The Mauser isn't stainless, just coated silver but that means that the barrel may well be harder steel.
Given the calibre, I would probably go for the Mauser as I think that it's a better system for longer ranges if you ever choose to go to a range for a bit of fun, etc. and the weight difference is negligible (Mauser is listed as 100grams more, I think). Yes, the barrel is harder to replace but a decent rebarrel is £800+ anyway. Mounting systems seem to be easier and more diverse for the M12 too.
Others have mentioned Shultz and Larson. They really are things of beauty (when using the three shot mags, at least) and probably the best finished factory rifle out there at the moment in my opinion but sticking to the stainless/synthetic theme you are looking for, the M12 just squeaks my vote.
Good luck, you should enjoy either.
Z.