I'm not to familiar with Montane as a brand but I've used a Patagonia R1 hoody with a Rab Boreas pullover on top. It seems like it has similar functionality to what you're talking about. When I'm backcountry skiing I run a bit warm with the R1 so if it's above 25 I use some other base layer. I dunno if that helps or not.
The valley floor is snow free and snowline is at least 2-3K above the valley floor in Winthrop. I bet there would be decent afternoon climbing on solar aspects, but it's been damn cold the past few mornings.