I use a Montane Fetherlite smock to keep the rain off. It packs down nice and small and will hold the rain off pretty well: you'll get wet eventually if you're out in the rain for a while, but it's good enough for the journeys I do. It's a nice bright yellow colour to help our myopic four wheeled friends out a little, and breathes quite well so you don't end up feeling boiled in the bag.
I've got some waterproof trousers from the same range, although they're black with shiney bits instead of yellow. They also seem to do the job.
Tbh, I'll often not bother to stop and don waterproofs depending on how hard it's raining .. it's often not as bad being out in it as it looks from indoors. Especially if it's warm.
I do wear padded cycling shorts for the commute, though that's more for comfort than anything else. I have a pair made by
Altura, another pair made by Montane. Both seem fine. Not sure about any performance increase: though I would need the throw off the cliff technique to improve my performance so I don't really have anything to compare to there.