You should buy the MSI R6670 ATI RADEON.Price is Rs 5096 excluding VAT.Unlike the Sapphire,HIS cards u listed,it also comes with one of the best cooling solution we've seen for GPUs. http://www.mdcomputers.in/graphic_cards.html
Apart from having the best quality components from msi,this card is also much faster than the GT440.And 2GB really doesn't matter at all,rather a waste of money when considering entry level cards.
7750 is a nice card but the availability in india is very scarce.Also the price starts from Rs 5700 and the OC ones will reach 6K so yes... if few more bucks can be spent the asus hd 7750 oc is definitely the way to go.
So far your CPU and RAM is enough for both the cards you're planning to get.
What power supply do you have?
for these cards you'll need a ~400W PSU(provided they're of a quality brand like corsair/cooler master,etc.)
Or if it be those cheap lowest tier frontech/zebronics,it should at least be 500W or above.
but I recommend you have the above option.