You could also buy nothing... i7 920/30 @ 4~4.2 is already pretty damn amazing
I suggest perhaps buying SSDs and/or more RAM, faster and more RAM, better RAD pump or anything like that, peripherals like mouse/keyboard/sound card/headphones/chair/desk.
If your 27" is 1080p maybe go eyefinity, or upgrade to a 27" IPS/PLS(samsung) 2560x1440/1600, if you want to go even further, you can eyefinity that.
ANYTHING but a 500$ CPU that you don't need
Seriously though, why even consider an i7 990X before an SSD?
P.S: I guess bad things haven't happened to me
But I donate because I feel it is my duty to do it, nothing more