Funny thing about windshirts: companies bring them in as a summer thing, but I only really wear them in winter. If it's raining, a wind shirt doesn't do a lot of good. However, when it's cold and relatively dry, the extra breathability of a windshirt is great. In winter, my primary layers are a thin wool topped with a windbreaker. It keeps a pretty great microclimate going for me. Cover w/a big poofy down piece as necessary, maybe an extra midlayer. Similar kinda idea as the Paramo gear, really...
WPB shells are just too hot for most aerobic output. Windshirts are a good balance. That said, in most conditions warm enough to rain, I don't really need as much wind/weather protection when I'm on the move. Therefore I don't get much benefit from a windbreaker in those conditions, but when the mercury drops I need to keep things dry, so a light WPB shell goes along. 40*F rain is no fun.