Definitely go with the layering.. Can get very hot going up hill.
Then fkn freezing on way back down.
A thin winshirt that packs down tiny always comes along too.
And thermal buff, in case of freezy extremities
Windshirt is good enough to keep off the worst of mizzle, even if it's not quite wet enough for waterproofs.
Legwarmers are handy, and never leave home without gloves in the winter even on a nice day.
Thin plastic ones at least cut the wind, under fingerless mitts, and keep off worst of wet.
Waterproof socks (effective dex shell - not slightly carp sealskins) do double duty as windstoppers.
3/4 length mesh lined waterproof trews are 'cool' enough to cycle in whether its wet or dry..
Most of these warmth / water repellent strategems, are taken in respect of Devon cycling, in winter, where if its not raining right now, then there's every chance it will be soon.