^+1. That GPU is not worth its asking price. I don't know what you have now, but it may be worth getting a second one for Crossfire (AMD) / SLI (nVidia) rather than getting a single GPU if it means spending that much.
Since you prefer nVidia and that board SHOULD have SLI support you're better off going with two 570s, or even two 560Tis, rather than a single 590. Of course two 6970s, or even 6950s if the extra shaders are unlocked, can be a more attractive option. Buying the 590 only makes sense if you are going to buy two of them or if you're board doesn't support SLi and you really want to stick with nVidia. In your case I say just get two 570s instead (or 580s if you can afford it) and be happy.