Asian tech site Expreview heard from NVIDIA that they won't release any GeForce GTX 275 reference cards. Add-in board partners who wish to launch a GeForce GTX 275 will need to design and manufacture the card on their own. This means there will be fewer GeForce GTX 275 cards on the market, but at least they won't all be nearly the same.
The first GeForce GTX 275 cards are expected around the date the ATI Radeon HD 4890 (RV790) becomes available, which is April 6th. According to TPU, the GeForce GTX 275 will be a card with 240 stream processors, 448-bit memory bus and 896 or 1792MB of GDDR3 memory. Clockspeeds are said to be a big higher than the GeForce GTX 260, but the specifications remain shrouded in mystery.