In reply to wbo2:
Yes, exactly, which is similar to what the Arc'teryx Proton (non-heavyweight version) is like.
The breathability for the likes of climbing in a piece like this is excellent (especially since you probably have a much less breathable - and totally windproof - shell on over the top).
I've used the Proton Heavyweight on colder days climbing and I'm glad I had it. Although not sure I'd want it climbing during close-to-freezing level on long leads. Although if I wasn't the one leading and standing at a belay for a long while, then it is perfect for that.
Standing about with it as a outer layer on a windy day though, not so much.