I second the GTX 650 (non-Ti)
If you were gaming at 1920x1080 with a faster processor, I'd have no hesitation in recommending the 650Ti. However, for that screen resolution, you could probably get away with something even cheaper, like an HD7750. As it is, you're held back by the PCI-e 1.0 slot, older DDR2 on a slow 1066FSB which has less than 1/3rd of the bandwidth of modern platforms. That's ignoring the fact that those feature-crippled Pentiums with smaller caches really struggled to prove themselves against much slower Core2 chips of the day (heck, the E6700 is almost seven years old now, and your Pentium can't even pretend it's that good).
Save your money by getting the cheaper 650 and putting the savings aside to upgrade your processor platform as soon as you can. You need
a socket 1155 system for serious gaming, really; Older (or AMD) platforms are fine for casual gaming but if you go by TR's metric, Sandy or Ivy bridge really are in a completely different league
. There's no point spending big bucks on a graphics card if you're not underpinning it with decent hardware, because those graphics card bucks are being held back by the supporting CPU/RAM.
Graphics cards come and go, but you'll use a processor for several years.