You can go for the 1gig version as u mentioned your budget is up to 6k, but honestly dont expect to be playing games on high settings with the 5670 on a 22" monitor, its adequate to play all games but dosent set the world on fire, have experience with 512 version on a 2 yr old 17" monitor.
If i were you would save up some more and go for the Zotac GTS450 which sells for around 7.5k here *techshop.in/store/zotac-nvidia-gef...card-buy-online-india-p-6674.html?cPath=320_4