In the right lane
Join Date: Dec 2005
Location: Des Moines
Bikes: 1974 Huffy 3 speed
You need to look for what is called a shell. These are somewhat wind-blocking fabrics. They won't block wind as well as your rain coat, but come pretty close. They won't help much with rain, but are generally less sweat-producing than a raincoat.
Still, with low temps of 40s, I would be tempted to try a wind-blocking vest with a couple of long sleeve polyester tee-shirts under. I carry the shell in my bag in case it turned nasty.