Never hunted AK, had one opportunity that fell through. If I were going for the species you are going after, I would take the 7-08, unless you WANT to be even more tired when you finally work your way through brush and onto the top of the ridge.

My experience is WATCHING AK hunts , but looking at the terrain on the Alaska the last frontier TV show, it seems like you could encounter a shot from point blank to several hundred yards. Personally I don't think you have enough time to "get real good" on 600yd shots, by this fall. There are tons of factors that come into play, and wind is the biggest. I HAVE hunted mountains, and I can tell you that on long shots, the wind can actually change 10-30 knots from your position to the target, as well as direction, at 600yds. Knowing the TSX's best opening velocity is somewhere around the 2100fps mark, I'd keep shots at 300 or less anyway.

With the 140gr bullet, the 280 will not give even 100yds more range, keeping to the 2100fps threshold. Now if you were using 160+ the 280 would have a slight advantage there.

Save the weight and your back.

Good luck.