An older thread, but I can't resist throwing in my $.02.
First, with the T3 action length is moot because they all have the same length action. The magazines are blocked and the bolt stop is different for the shorter calibers but the basic hardware is all the same dimensions.
Second, of the two calibers in the original post I suggest 7mm/08 but it's really a toss-up.
Third, elk will fall nicely to all of the calibers suggested IF shot placement is correct. I have taken elk with 280, '06, 35 Whelen, and .444 Marlin. None went over 75 or 80 yards after being hit and all were dead when I got to them.
Fourth, for long sessions at the range a seven pound rifle is going to get a little tiresome quicker than a heavier one. I FINALLY learned to wear a PAST shoulder pad at the range for all calibers above .22 LR. It allows me to concentrate on my shooting for a longer period of time. As we all know, recoil is imperceptible when actually shooting at a game animal in season.
Finally, I recommend you keep your '06 and use it in Colorado. Get a good gunsmith to tweek it and sub-2" groups should be the norm. Besides, no one needs a MOA rifle to kill big game.