In 2 years, alot of popular GPUs today may be obsolete.
Oh and you can always add in another 670 into the mix which will effectively give you the performance of a $1000 card.(690) IMO, 15 FPS is a good amount of FPS loss, but thats just me and my personal needs. XD
Adding another 670 adds in more issues with SLI, although nowadays its much better working, its a hassle and finding the card to crossfire is another story.
15 FPS Is a loss, But i dont really record fraps or anything so it wont matter to me.
Also PCI-Express 3.0 came out this year with the mobo's. The cards we have this year dont even use the technology behind pci e 3.0 so i think waiting a few years would be much better.