Re: Hunt coming up, about 1000 meters expected
If it were me I would be torn between what was powerfull (300 RUM) and what I was most familiar with. If you say you have fired the 308 to 1k I would probably go with that provided I had a suitable load for it. You have a 26" BBL so you can get good velocities accuratley with it. I know from first had that its hard to get bullets like the SMK up fast enought to perform well on game to 1k. A 155 SMK or 178 AMAX might do much better than a 168 or 175, I know for sure the 190 wont expand on a deer fired from a 308 at that range. The 155 might, the 178 most likely will but dont know. However accuracy is most important. I would go with what you shoot the best with.
Remember also if you have a tight twist, like a 1-10 and shoot loads like a 155 or 175 or 178, these will perform better than expected upon impact vs a longer bullet. The faster you spin a bullet more than neccessary, the more it will break up.
Hope that helps a little
Long range shooting is a process that ends with a result. Once you start to focus on the result (where the shot goes, how big the group is, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.