I had a stormex on my CBR 600w (1998) before my garage was built and i bought my MT. I think it was medium but don't quote me on that. Considering all the shit rep that Oxford products get i was really pleased with it. It had a fleece (kinda) type liner and kept the bike dry without making it sweat and condensate. As TT says, breathable is the main thing, if it condensates then it may as well be in the rain.
For the money i'd recommend it. However after a year outside in strong winds it did rip in the end. I'd say they were disposable and replace it after a year. Thats my 2p worth anyway.