Jaydip, no I didn't think for a second that HD7990 at $999 was good value. I even said when it launched a person is better off getting 2x 670s or 2x 7950 OC or 2x 7970s. At $579 now vs. $1000 GTX690, it is way better value.
I think you missed my point that NV keeps charging way higher prices in US/Canada and since gamers keep buying their cards, NV has no incentive to lower prices. That's all.
GTX460s were excellent overclockers. A lot of them can hit 850-875mhz and some can hit 925mhz at which point their performance was near HD5870 or faster in some titles. If I were you I would overclock them and hold out for 20nm cards given that you said they play your games well already. :thumbsup:
If you are going to be overclocking I would switch.
HD7950 oc is going to be 6-29% faster than 660Ti oc. Additionally, if you get the 7950, you also get 3 free games. If you don't have those titles, then there is more incentive for you. Otherwise if those free games don't matter and you won't be overclocking, then keep the 660Ti and wait to upgrade on 20nm.
Or since you already know how to overclock based on your 460, you could get a
$268 Asus DCUII 7970 (due to 7% off discount off $309 price + $20 MIR) and overclock it to 1050/6000.