In reply to si_pritch: Montane Prism is one of the best layers I've bought so far !
Base layer with a Rab Boreas pull on when its windy, and then when it gets super windy or stopping for lunch throw on the Prism and if it rains light put a soft shell on over that.
Find that 90% of the time you won't need a full blown GT waterproof unless it starts pouring and can get away with a super light, packable shell !
I've had the Prism drenched while caught in a shower walking the dog and found that although you can feel the wet through it, i.e uncomfortable, I never felt cold (the joys of primaloft)