Nor do you want to match a GTS 250 512mb with an I5 build ...
The GTS250 is basically an 8800 series card, better cooled, and overclocked ...
The technology is honestly too old.
The BEST bang for your buck card on the market is an Nvidia GTX260 (216) core, with some of the overclocks on this card reaching near GTX280 speeds, especially at resolutions lower than or equivalent to 1920x1080.
I would personally prefer to go for a 5850, but stock issues and the $70 price difference may come into play.
Also I've used the Cooler Master TX2, and whilst a perfectly respectable cooler, it's probably really worth spending the extra $10-20 on a good cooler, which will allow much more significant overclocks on your I5, which will certainly assist your GPU if you decide on some of the newer tech's, and from the reviews of how easy and stable the new Intel chips overclock, will be a rewarding experience too.