For 40 degrees, I'll go with lightweight tights, long sleeve jersey, full-finger gloves, and tights over shorts. Performance Bike is the easy and inexpensive way to go.

On the way down to 40, arm and knee warmers take me down to 50, maybe 45 if it's sunny and not windy.

You'll figure out your own warming scheme with a little practice, and then the temperature is the first thing you'll check before dressing in the morning.