Forget nVidia, close your eyes and purchase an Asus 7750, 1GB GDDR5 edition. Best performance for money card at 7,000/- .
Full 3 years warranty too.http://www.flipkart.com/asus-amd-ati-hd-7750-1-gb-gddr5-graphics-card/p/itmd7hzcp7hsqpzj
You can get this card for little less money, if you check with your local computer shop dealer.
PS:- If you still want nVidia (not a wise choice for this price segment), you can get a Geforce 640, 1GB GDDR5 for around the same price.
For both AMD/nVidia cards, YOU DO NOT NEED more than 1GB of graphics card RAM.