I had an interesting experience with a windshirt (it was Houdini, but guessing it would be the same as any similar windshirt). A buddy and I were bagging a peak in early spring on snowshoes. It started to light rain (both of had windshirts on), it stayed light rain for over an hour all the way to the peak. Windshirts wetted out completely and as we started down (not working nearly as hard) we started to get chilled in the wet windshirts. We grabbed our hard-shells and thrown them over (the wetted out) windshirts. Roughly 45 minutes to an hour we stopped for a short break and unzipped my hardshell to check on the windshirt. It was bone dry! Ditched the hardshell and put back on the perfectly dried windshirt (it had quit raining by this time too).
Anyways, pretty cool experience and one that I've filed away for a future trip. Not saying the results would be identical each time, but windshirts do dry quickly and probably a lot of body generated heat forced through the base layer and through the windshirt (all under the hardshell).
