asus P5GC-MX with UMAX 450W smps. Are the above good for both of them?
Well your motherboard maybe, but definitely not your PSU. Its a crap local one which would lead you frustration, constipation, sleepless nights, financial doom!
Get Gigabyte Superb 460W - 2200 INR - 2600 INR.
Change it before changing anything.
HD4670 is a better. HD4650 is not worth buying. Also it depends on your monitor. Which monitor do you have.