It's an odd time to buy a PC right now.
As fred has mentioned, The 580GTX will be old hat very soon with the release of the 680GTX, If you're an nvidia fan that is.
Rumours have it in April and maybe even early april (like the 8th or so) Ivy Bridge should ship to retail. Prices could be totally fucked though since it's new tech, along with the pricing for the 680 but it will be an increase in performance over what's currently on offer. Ivy bridge is meant to be 30ish % quicker over current Intel offerings. That's all heresy and rumours though since there's still no reviews.
Patience might be the best option for the next 2 weeks unless you really need a new rig.