Likewise, I've sat out a blizzard high up in the Lakes in just an Extreme over bare skin, but I almost never use it and the only reason I won't sell it is because it has stories attached to it. And it smells.
I think the Hydrogen is about 500g or so, which makes it half the actual weight of the Extreme, but it really does breathe and regulate much better. I've yet to ride in the Montane, but I have a Rab Alpha Direct which is the same combination of materials - Alpha Direct with a thin Pertex shell over it - and I've ridden in that through a couple of winters now. No clammy feeling at all even when puffing uphill on the MTB maybe with the zip half open if you really need it, but keeps you warm and toasty on the descents. It's the only jacket I can just leave on all day over a base layer and never feel the need to mess with it - honestly a revelation.