Maybe someone else has some good recommendations. Your power supply is the limiter, although I always hear Corsair can go above their advertised wattage, I'd personally not do it unless I had to. The GTX 460 is a much better card than the one I mentioned but asked for 450W... I'd ask some experts if they think that is wise with your supply.
Alternatively, you could up the PSU and then get a nicer card.
for your psu 400 watt... gts 450 or hd5770 , since its a corsair you might get away with a hd6850 ... but it'd be pushing it... if you want a gtx 460 , or a 6850/6870i'd reccomend going up to a corsair 550VX
I see the HD6870 uses less power than the GTX 460 1GB. I'm going to wait for the GTX 560 release and see how it compares to the HD6870. Found this thread: http://hardforum.com/showthread.php?t=1540093 so hopefully OK on power supply. If I have to upgrade the power supply I know I'll probably be tempted to SLI/Xfire
No problem, just remember, the harder you run your power supply, the faster it begins to degrade. So best to get the card that is the closest to the 30A you have. I had a card that required a little more power than my advertised PSU rate, but it ended up working, but a year later I had to get a new supply to continue running the card (the computer was fine, just not load with the card). Corsair is better though.