Several online retailers are already listing Nvidia GeForce GTX 500 Ti cards.
Softpedia reports that numerous European online retailers are already listing Nvidia's yet unreleased GeForce GTX 550 Ti graphics card, indicating that it will be an overclocked version of Nvidia's previous GTS 450 release which featured a GF116 core manufactured with the 40-nm process.
One GTX 550 Ti card offered by PNY is listed here, featuring 1024 MB of GDDR5 on-board memory, a core clock of 900 MHz and native support for DirectX 11. Other features include a 128-bit memory interface, a shader clock of 1800 MHz, 192 stream processors, shader model 5.0 and 32 texture units. The memory bandwidth has increased from 57.5 GB/s offered in the original GTS 450, to 65.5 GB/s in the current card.
Additionally, the GeForce GTX 550 Ti will feature a dual-slot form factor, have a maximum power consumption of 110W, and support HDCP and SLI. The card is expected to be nearly equal to the Radeon HD 5770 in terms of performance and slower than the Nvidia GTX 460 card with 768 MB of memory.
Currently the card is listed around $216 USD, depending on the vendor. This is higher than the GTX 460 which retails around $150 USD or more. But as Softpedia points out, many retailers list unreleased hardware higher than the recommended prices offered by the manufacturers.
As the card hasn't been officially announced, we'll have to play the "wait and see" game in regards to actual pricing, availability and specs.