Your 1090T@4ghz should be more than good enough. No need to worry about that.
If you're not too bothered about antialising, or running upcoming games at their maximum graphical settings then you should be ok, for a while.
If you wanted to run at 2 or 4xaa & max out the graphical settings in gfx intensive titles like Crysis 2 , BF3, etc... then I would consider a gfx card upgrade.
Just remember that the 7xxx series cards are due in Nov / Dec this year afaik, so if you're happy with what you have at the moment then just wait for them before considering an upgrade.