In reply to Milesy:
I've had a R1 Hoody since 2008 and have worn it on nearly every winter/alpine route I've done since. It is still going strong and is one of my favorite bits of kit. The long body, long arms with thumb loops and balaclava hood eliminate gaps and cold spots.
If you want the ultimate in warmth for winter climbing, combine it with a pair of powerstretch bibs (like these:
http://rab.uk.com/products/mens-clothing/fleece/ps-bib.html) and say goodbye to any cold spots.
The hood is excellent and since having it I have never experienced that horrible feeling of spindrift pouring between the gap between your fleece and balaclava.
It's interesting to read the comments about the thumb loops. I wonder if these posters have longer arms than me? I always use the thumb loops as they keep my wrists warm and consequently reduce the number of times I expirence hot aches.
I've recently acquired a ME Eclipse Hoody, which is 1/3 cheaper than the R1 at full retail, £90 compared to £120. I'm yet to use it winter climbing but have been using it a lot for cycle commuting recently.
It is very similar to the R1 Hoody, with a deep front zip, balaclava hood (the one on the Eclipse is even better), long arms with thumb loops and a long body.
However the fabric is quite a bit thinner than the R1, so I would probably want to add a second fleece layer when I started the route.
Also the sizing is a little different. I'd take Medium in an R1, but would be a Large in an Eclipse.
HTH.