I find that my legs above the knee get coldest and have resorted to stuffing free newspapers down my over trousers on one occasion.
I have definitely found that wearing too many gloves or socks will constrict the blood flow and, for me, result in cold hands and/or feet (Exeter 2011 or thereabouts down to -11degC)
On the Exeter this year I wore a one piece rain suit over a lined Enduro jacket and lined Enduro trousers, with fleece, sweatshirt, merino long sleeve shirt with cotton T under, and long john type running pants under the trousers. With a Buff neckerchief, balaclava, full face adventure lid, silk inner gloves, crappy cheap fabric riding gloves (plus a spare pair stowed away), and gore-tex overmitts I have never been so toasty. All the removal options are there as well if it gets too warm (as it can do on the LE) so bear that in mind.
I like cotton next to my skin if possible, being a delicate flower, otherwise I generate enough static to run a set of auxiliary lights. I think light layers are the key.
And 10 yds of trying to bumpstart your bike guarantees heat.