You don't need a slipper for road use. And they need careful setting up for the individual rider. If you mostly ride on the track, that may be a different matter. But, y'know, those DD guys manage with a stock clutch...
I've got an STM 48 tooth basket (conventional clutch, not a slipper). I got it from Nelly at Cornerspeed. It's a better engineered job than the stock clutch, but you need STM plates to go with it, and it's more expensive. I bought the set of plates and basket (you use your stock hub) for about 250 quid IIRC, but the basket separately is about 170 quid. It's a nice anodised aluminum job, and lasts longer than the stock clutch parts, so that offsets some of the initial expense. I was chatting to guy yesterday who races a very quick 996, who's got an STM slipper (same basket as mine). He said he used to get through three stock baskets per season, but his STM basket is lasting him into his second season
[Edited on 14-5-2006 by moto748]