In reply to:
Recently, I started climbing on double ropes (8.5mm). The regular ATC is not the best choice for this application, though you can add another biner to increase friction. The Reverso works well, but the Trango B-52 I bought recently seems to work better with skinny ropes. The advantage of the ATC-XP over the regular ATC is similar, more friction when you climb with skinnies.
With the three devices I own, I carry the B-52 most often.
