Your 6.5 would do the job under ideal to good conditions. And I am a huge fan of the little mauser as a deer rifle (also the 6.5x57). I have both and they are lovely little things - for deer. I also would not even think of lugging a .375 around an Asian mountain in winter and at altitude (and I love the .375). Were I traveling that far with that much invested in a hunt, where my one an only shot is just likely to be in marginal conditions and at very long range, I would opt for a cartridge and rifle which would give me every possible edge. In my rifle rack that is a .300 WM on an R8 action with Leica 2.4x16 securely in place. If I had the same rifle with a .300 Weatherby, .300 RUM, or .300 Lapua barrel, I would likely take that.