what is your PSU? Your CPU isnt completely useless... what are you play? at what resolutions?
Your CPU will probably limit your fps, but I would still max out your gpu budget of Rs. 10000 assuming your PSU doesnt limit you. Or maybe get the 7750 and 2 more GB of RAM.
I today installed FIFA 13. It worked like ***, everything cartoon. I am a bit much irritated at my CPU. I just wish I could throw it away. By the way I need it for games like FIFA 13, Arkham Asylum, AC-Brotherhood. I am not a hardcore gamer so low to medium settings would do. But something that I can't seriously tolerate is lags and cartoon graphics.
And for my PSU, is the power of the PSU the input power or the output power? Its written 450W on the inside but I still am not sure of it.