I have 140mm Revs on mine. For a while I had U-turn Pikes and tried in various settings: 110/120/130/140.
It's just a compromise.
120 is noticeably better for aggressive climbing on steep/loose stuff where you need to be seated for rear wheel traction. At 140, the front end can be a bit light and wandery on really steep stuff, but it has to be incredibly steep for this to become a problem, not something I encounter very often at all. Also, if there's enough grip to allow you to get out of the saddle, then it's a non-issue. The ASR-5 seems to encourage you to stand up and pedal harder! Going down, 140mm feels a lot nicer to me. Slacker, faster, just great for charging.
I ride mainly in the peaks, but I took it to the alps last year. I suppose if you mainly ride smoother stuff and you're not as aggressive then 120mm or 130mm would probably be better, but I've certainly got no plans to change mine (which would just be a case of adding an extra spacer to the fork).