You should ignore things like memory bandwidth, core clock etc. You don't judge by those.
Only three things matter -
1) FPS in games.
2) Power consumption.
3) Price.
Thanks for your suggestion.
It's already out a week ago. Google.
I found this source-
AMD Radeon HD 7870 and HD 7850 Launched - 3D Tech News and Pixel Hacking - Geeks3D.com
HD 7870 has much better performance than other GFXs of its price range. Especially, as compared to GTX 570, it has better performance and yet its quite cheaper. It also has variably good performance as compared to HD 7950 and GTX 580, which possibly be matched by an OC edition of HD 7870.
But because nvidia kepler series are going to be launched in a month, so i think that i should also wait for GTX6.X.X. Take a look at this link-
*www.brightsideofnews.com/news/2012/2/10/real-nvidia-kepler2c-gk1042c-geforce-gtx-670680-specs-leak-out.aspx
It says that GTX 660(GK104) would have an approx. cost of $250 and will perform better than HD 7950. So, i may be able to get something better than HD 7870 in a price of $350.
But 1 thing is want to ask is that will my Gen2(PCI-E2.0x16) mobo [MSI Z68MA-ED55(B3)] will support these PCI-E3.0x16 GFXs.