I've always used Endura 3/4 thermal bib tights, nice and warm- started wearing 3/4 Hummvees, though- see how good they are, certainly pockets come in handy.
Buffalo jackets are Big Dogs Bollocks when it comes to keepin' warm and windproofed- I have a mountain shirt, with all zips and vents, ye can accommodate a fair temperature range. No cheap, though. **ye might find the 'special six' forces issue at a good price used/surplus**
Above all, I'd agree with the chaps above about toes, fingers, and especially ears- sleeve off an old thermal top can make a good enough headband/hat- like a Buff, but for nowt! Decent gloves, socks, and shoes will do more to keep ye comfy than a jacket will whilst yer riding- ye tend to find that as long as ye have something windproof at yer chest, ye actually need to be letting heat out as ye ride- a gilet with mesh back panels can do ye well in even low temperatures, but ye will need summat warm to put on when yer stopped.