We've gotten off topic a little. The OP's question was whether or not the 120 TTSX is a good whitetail bullet out of a .280. The answer is it's an excellent bullet for whitetails.
When I got a .280AI I tried Barnes 120's 140's and 145's. My rifle likes the 120's better than anything and they will kill the living hell out of a deer.
If I was shooting past 400 yards or shooting at an elk I'd do something different but I'm not and I doubt that AUM is either.
Goatkiller I don't ever hunt with a 30-06 but I do shoot 110's out of my .308 most of the time. Sometimes I do go all the way up to 130's though.

I agree with Joshm28 too..... if I knew a gunsmith that wouldn't charge me an arm and a leg I'd ream that chamber out to 280 Ackley. That will give you a big jump up from a 7-08 if you ever start shooting big critters way off and you actually need heavy bullets.