I'm also curious to hear about Koss... would like to make the switch to soft shell raingear but am a little skeptical because I've never used it.
The softshell stuff I have I would not consider rain gear. It is water repellent but far from water proof in anything above an intermittent drizzle. Personally, I'd shy away from anything but a lightweight "actual" rain coat. Anything softshell would also be too warm a lot of the time.
I've heard that Gore Windstopper is mostly the same as Gore-Tex without sealed/taped seams. I can't verify that. I do have a Sitka Jetstream Lite jacket that is windstopper and it is more water resistant than other shells, but still not water proof. Also not at all breathable.
Just some(sidetracked) hopefully useable info re: softshells and rain gear.