I have no plans on using AA or AF so I probably don't need a really expensive video card. There seems to be a good bit of back and forth on if I can run a better card of not with my current power supply.
the PSU in your SG05 is a legit 300W unit, we were worried it was some old/dated/cheapo POS, and since we also now know its a small form factor unit, we also then know you're not plugging in dozens of peripherals to suck juice from the PSU.
I'd concur with what someone else said, you could start looking into the GTX460 and Radeon 6800 range as long as they aren't overly long
I'd say unless there is a particular reason for going nVidia, AMD would net you better performance per watt and that a 6800 would offer you the best overall value