I'm going to share a piece of advice which is fairly well known in the hiking (especially the winter hiking) circles but a. isn't as widely discussed in the cycling circles and b. may not be as applicable.

Your primary goal in cool and wet weather should be to stay warm. Now, staying dry plays a big part in that but through experience you'll find it that it is IMPOSSIBLE to stay dry. You want to minimize your sweat output, so start out dressed such that you're a bit cold because as you go you'll generate a lot of energy and you'll warm up. If you are warm at the start, you'll be much hotter once you get going, you start sweating, and if you can't take a layer off, that's that. Hiking uphill = dress very light, on flats and downhill = put on a layer. Now, I find that this approach works for hiking but is a bit tougher to dial in for cycling because of generally higher strain to warm you up and higher average winds to cool you down. So you need to combine clothing that traps heat with clothing that blocks wind. The trick is not overdoing it.

No, where am I going with this? In my experience I found that you need waaaay fewer/thinner layers than you think. For me during moderate and high activity a rain shell is equivalent to a 100-weight fleece in warmth! If you're sweating in a 'clamshell', take a layer off. If you can't, unzip vents. If you're still hot, consider wearing a warmer, much more breathable, but only water-resistant layer instead (hey, did you mention wool?)