Mainly it depends on the temperature ( not just when I leave, but over the course of my ride ... which sometimes means how long I'll be out ) and how much stopping I plan to do. If I'll be going straight to or from work, it's less important, because I'll work up enough heat after a few minutes to stay comfortable throughout the ride; if I need to stop a lot, my core temp is going to do a lot of yo-yo'ing, and I may need more isolation from the elements. But, really, if it's above 50 degrees, unless there's going to be a lot of wind, a wool base layer is plenty.

You might be wrong about the jacket, though. I have an Arc'teryx Accelero for the kinds of conditions you describe. It's not 100 % waterproof, but more than enough to wear kayaking on a rainy day. More to the point, it breathes like magic, and doesn't add any more warmth than it needs to, eg more than any layer would. It allows some wind and air to pass through, so the breeze from riding is nature's air conditioner. Here's the point I'm getting at: I've never felt warm from riding in this thing ... the only time I sweat when I'm wearing it is when I stop, because I've lost the cooling wind.

Now that we're talking about clothes, though, wool keeps its insulating properties when it's saturated, and has a way of not feeling wet. Merino can be made softer than cotton.