In reply to Arjen:
> (In reply to Couby)
> Can't really recommend heavy merino for scottish winter, if at all I'd go for the thinnest one you can get. Heavier ones get heavy and wet, and they're not really warm that way.
Not encountered this problem myself -- Icebreaker base-layers (190 and 260, iirc) are pretty light-weight. To some extent what works best will be dependent on the outside temp, what other layers you wear, and how hot/cool you run, and how much standing around on stances you do.
And having started climbing in the '70s, I can remember using old heavy wool when I first went winter climbing, then changing to synthetic when that got established, but now that merino is out, it'd take something pretty revolutionary to get me back wearing sythetics.