its good to see strong specs ... thats half the battle won when upgrading your graphics wrong and the core i5 3570K is a pretty damn good cpu ... also 8gb ram is plenty aswell
well at the $250 price range i would recommend the "GTX660ti" .... this is a impressive card ( maybe slightly overpriced ) however it performs well and will compliment your core i5 pretty well ..... it also has a pretty low power requirment (450w min ) which considering its power is quite good
it has 1334 cuda cores and a 192bit memory interface and the 915mhz core base clock can be ramped up to 980mhz using turbo mode
however its the effective memory which blows me away with the GTX660ti ... the 1gb/2gb of gddr5 memory runs at a insane 6000mhz (effective ) which is crazy even in gddr5 standards ... and this results in a healthy 144gb/sec memory bandwidth making it ideal for high res gaming (1920x1080 )
the GTX660(non ti ) is also a good card .... however memory clocks are significantly lower were as core clocks are higher .... the GTX660 is probally a better option for sli configurations ( especially with the price ) however i would still recommend the GTX660ti for a single card configuration
both cards will have no problems with your corsair 750w psu .. infact the GTX660 in sli would still have power to spare ( 650w sli for GTX660 ) ...
also both cards use a 28nm gpu which will keep tempertures low under load .... and fan speeds quiet