If you are hunting in the Highlands, with the distances involved and the game available, then you can't do much better than the .308 (or 7.62 x 51, 7.62 NATO, etc., etc.). In fact, for hunting throughout the UK and Europe as well, you can't do much better.
You can't do much better than a Tikka T3, either.
If you simply want an additional rifle (and who doesn't), or a different rifle.... well, that is another matter indeed. The possibilities are almost endless.