well, if u can increase your budget to rs 1000 more u should go for hd 7750 it is rs 7300 in flipkart and will surely outperform both 630 and 6670
it also uses less power so go for it and before buying check that your psu is capable or not for handling them
i'm also planning to buy hd 7750 this year and it can play black ops 2 at high settings................