Toms Hardware - http://www.tomshardware.co.uk/Nvidia-Kepler-GTX680-GPU-geforce,news-37545.html are reporting rumours of an early release to combat the 7970. Nice if true
The general consensus still says not for a few months at least. Maybe get low and mid range cards first, top of the line following in the summer or autumn. Considering AMD decided o only launch the highest end card first then a month later start releasing cheaper cards it seems to suggest not many chips are making it out of the factory floor right now, and if Nvidia decide to launch early i can expect the unavailability to only get worse for both sides until production really gets into gear.
Funny how these rumors have appeared now that AMD have done a hard launch of the HD7970. I wonder if nVidia would have any interest in spreading those rumors to deter people from buying from the competition. Nah....
