I've had my share of 260's...
Go less than 22" and they get blasty IMO, and speed does fall off quite a bit.
When I rebarreled the Montana, I went 23", mostly just to hang another few ounces out there for a little extra shootability.
All that having been said, on the T3, I'd take a serious look at the Swede. Get the LA mag, and bolt stop while you're at the retube job and rock on. With data from Speer in that action, you get an extra 100+ FPS across the board over the 260.
