I am a value oriented PC builder/gamer and i rely on mid grade gaming products and overclocking, but if you happen to have a 550 Ti with the current drivers and have attempted overclocking you will notice you cant go over 999 Mhz using any tool but the card is known for having safe and stable Ghz clocksY. I am posting this to save anybody who reads this their time by saying it is a limitation set by NVIDIA, the only way to completely "unlock" your cards capabilities is to use an old driver, which the latest without the limitation is 296.10.
So here is a link to the driver you will need
http://www.nvidia.com/object/win7-winvista-64bit-296.10-whql-driver.html
Just putting this on here because this took me days to figure out