I looked up the Overdrive 8.5 specs on the severn website and it looks like a nice sail. Very similar specs to the NP RS slalom.
I couldn't find the actual weight of the sail on the servern website, you wouldn't know it off hand would you? This is an important item to me when comparing sails not sure why it isn't listed.
Also, I've noticed a lot of the formula race sails have 4 cams. Is there a huge difference in speed having 4 cams vs 3?