Experimented with clothing, but it wasn't as bad as I had feared (at 43F).

Wore lightweight polypropylene long underwear as my base layer.

Wore my ski gloves, and they were probably a little too much, but they kept my hands toasty warm. Those would probably be good down to teens or single digit temps. Note to self: buy winter cycling gloves.

Neck warmer was essential, otherwise would have turned around at the end of the street. Pulled it up over my nose & ears, and was comfortable. Only down side is my glasses kept fogging until I started exhaling out through the neck warmer.

My head was warm enough, even though I didn't wear a cap under my helmet. Just to be safe, I ordered a thin one to wear under my helmet for a little extra protection from the elements.

Wore windproof cycling pants - worked grate!

Wore a heavy fleece top, and the wind blew right through it. Felt cool, but not uncomfortable. Ordered a windproof jacket shell tonight.

Overall I was very comfortable, so I'll keep riding in 40s & 50s. Might even try riding in the 30s...