gtx 650ti 1gb which brand should i buy ???

Then the 650 Ti would be a decent value for you for sure

The Palit version is pretty good too

http://www.flipkart.com/palit-nvidia-geforce-gtx-650ti-1-gb-gddr5-graphics-card/p/itmdh8dypkcjhzpf?pid=GRCDH8CZ9FM4AKRG&otracker=from-search&srno=t_1&query=gtx+650+ti&ref=b791c092-8fa6-47dd-85f3-5c83a3dfe73d

Just make sure your PSU has over 20A on the +12v rail (look inside at the PSU sticker) and that it has a 6 pin PCI-E connector

If you have enough amps but no connector, you'd need an adapter

Seems that the Zotac card actually comes with an adapter, awesome

http://www.flipkart.com/zotac-nvidia-gtx-650-ti-1gb-1-gb-gddr5-graphics-card/p/itmdezd6yn6kwa7m?pid=GRCDEZ49PTZU4G7E&otracker=from-search&srno=t_4&query=650+ti&ref=af342f23-c590-414e-a8e9-e45d0f216f28

There's also a 7790 in that price range which is about 10% or so quicker than the 650 Ti
 
If you can find another Sandy Bridge i3 or i5, then yeah you could, or an Ivy Bridge CPU after a BIOS update (do at your own risk)

Either way, at your resolution you should be fine, just make sure your PSU is sufficient as I mentioned

(Just make sure your PSU has over 20A on the +12v rail (look inside at the PSU sticker) and that it has a 6 pin PCI-E connector

If you have enough amps but no connector, you'd need an adapter)