I doubt there will be any availability problems due to low demand in this price category and the maturity of the process node. And of course a lot of people will simply wait for Cayman before making a decision. This still won't be the fastest card around when Nvidia touts it as the fastest GPU. 15-20% is easy with the full 512 cores and some architectural tweaks, no need to go about cutting any GPGPU stuff. I'd be shocked if something like that happened after Nvidia has put so much effort into Cuda marketing.