Those kind of temps, I generally just deal with being a little overheated when it warms up. I think it depends mostly on whether you deal better with being too cold or too warm. #1 on my list would be a thin cap that will fit under your helmet without adjustment, and stashed in a jersey pocket when it's time to lose it. I'm always amazed at how much difference head covering makes. Light shoe covers, just to block the wind, shouldn't be overly warm when it does warm up. A microweight wool base layer under a LS jersey, and a windblocking jacket or vest (or convertible jacket/vest). Legs are my biggest problem. I don't own wool leg warmers, but if I were going to be doing that kind of ride at all regularly, I'd probably get a pair.