The NVIDIA GeForce GTX 550 Ti is disappointing. For most of the Linux OpenGL tests carried out, the factory-overclocked GeForce GTX 550 Ti was slightly behind or right on par with the AMD Radeon HD 6770 graphics card, which is using a Evergreen-based GPU. The only test where the GeForce GTX 550 Ti came out ahead was with Unigine Heaven, but based upon the other NVIDIA and AMD numbers for this tech demo, there is likely a Catalyst driver regression to blame for this Radeon drop. Even so, overall the EVGA GeForce GTX 550 Ti with its ramped up core, shader, and memory clocks while carrying a $140 USD price tag could not always keep up with the Radeon HD 6770. There's Radeon HD 6770 graphics cards from many different AIB partners for less than $110 USD. With various mail-in-rebates and other sales, it is easy to find Radeon HD 6770 retail cards at $99 or less. Not only was the Radeon HD 6770 frequently delivering noticeably better frame-rates, but it was also operating at a lower temperature and consuming less power.
Also to the benefit of the Radeon HD 6770 graphics card and the other AMD GPUs is the official open-source driver, compared to the GeForce graphics cards only being supported by the community with an open-source driver that is made through reverse-engineering the proprietary NVIDIA driver. For Fermi hardware such as the GeForce GTX 550 Ti, if using the open-source driver you need to be using the Linux 3.1 kernel (or newer) for self-generating FUC microcode (or generate your own microcode from a NVIDIA binary dump), there is no upstream re-clocking support, there's no Nouveau dynamic power management that's fully reliable yet, and the Gallium3D OpenGL support is still under active development. AMD Radeon hardware is still the definite win if wanting a discrete graphics card with a fully open-source Linux driver stack.
About the only advantage the NVIDIA GeForce GTX 550 Ti would have under Linux compared to the Radeon HD 6770 or other AMD offerings is the PureVideo HD support that is exposed to applications by the VDPAU API. NVIDIA's video acceleration implementation is still superior to what is offered by AMD with the far less popular XvBA interface for tapping the UVD2 engine on modern Radeon graphics processors. However, if you're wanting a graphics card for just an HTPC / media center, you wouldn't want the GeForce GTX 550 Ti due to its warm temperature, high power consumption, and a low-end NVIDIA GeForce GPU is more than adequate with VDPAU for current HD content.
Hopefully NVIDIA's next-generation mid-range Kepler graphics processor will be more interesting under Linux when it's released in a few months.