I'm gonna both support those that think wind chill factor is important for biking, and also confirm my own opinion in the OP.
I will start by paraphrasing the OP:
Wind chill factor ... has very little effect when your riding a bike ... a wind block layer is part of my winter kit any time the temps are below 45F/8C, regardless of the wind speeds (or wind chill factor) because riding a bike is creating a constant 10-20 mph wind (16-32 kpm wind).
I have a piece of winter kit will not wear in the colder conditions (under 25F/-4C wind chill): my
45NRTH Greazy Cap . I love this cap and wear it a ton for temps between 25F/-4C and 50F/10C; however, the cycling bill on this cap channels cold air to my forehead, giving me a brain freeze headache. I'll wear a wool skull cap (without bill - see OP pic) in colder/windy conditions; and with air temps between 25F/-4C and 35F/2C, I will consider wind chill factor when picking skull cap versus Greazy.
OTOH my forehead is
bare skin and that's the point of wind chill factor, how the wind can affect exposed skin. So, wind chill factor works for bare skin, but ... and I repeat what I've said a ton ... when temps are low enough to consider wind chill, you'll have very limited skin exposed while riding a bike, so it's pointless.
For reference, me with my Greazy cap at the low end of it's temp range for me.
