In reply to Glyno:
First came across Buffalo gear over 20 years ago when (knowing nothing about it) I borrowed a special six shirt from a friend and then did something that involved me being dunked in freezing cold water for 5 minutes sometime in the winter.
I got out thinking right, I need to sort something out quickly before I freeze to death, and in the few minutes of running around I sudddenly noticed that I wasn't even cold, and more to the point didn't even seem wet!
Anyway, years after that when I started doing Scottish winters and knew a bit more about it I loved the simplicity and toughness of one outfit of the stuff so bought the whole lot - shirt/hood, salopettes, belay jacket/hood. TBH, I only wore the salopettes once, they were just far too hot in almost any weather for Scotland. I used the shirt and hood for years, but always carried a light waterproof and belay jacket as well as the Buffalo belay jacket was heavy and bulky, and couldn't quite get my head round not having a little bit of spare clothing - although I rarely ever used them, even in driving rain or freezing conditions as I did find that the shirt deals with it very well if you keep moving.
I love the shirt, it's brilliant, but I have to admit I don't use it so much now, and think you can get better choices and materials (I use base layer/mid-synthetic layer/outer softshell and carry a light waterproof and belay jacket nowadays) in terms of materials, comfort, and fit - although that does come at a much higher cost.
If you're set on it I'd say buy a shirt and hood first and see what you think by slotting in into your clothing system as a replacement for a base layer and mid/outer and see what you think. If you feel the need to wear a base layer with it I reckon the Brynje mesh ones would work well.
In terms of pile/pertex gear both Montane and Buffalo have good and bad things about them in terms of style/fit/materials but both work fine, so I'd try both on and see which one you get on with best. FWIW I found the Buffalo fit much better on me, and a bit less faffy design wise - although please don't pair it with a pair of Ronhills like I used to...
Post edited at 10:17