best GPU to pair with Phenom x2 550 to run dota 2 at max settings? (i know my cpu is old)

[stubz17]

so i am currently looking to buy a gpu specific for dota 2 so i can run it at max settings..i have a phenom x2 550 not oc'ed, 4gb ram, 500w psu and a gt 630 4gb ddr3 pls i need your godly advice 😀 tnx!

 

[clutchc]

It would be helpful to know;
1) your budget
2) the make/model of the "500W" PSU. (not all PSUs are up to their ratings)
3) your monitor's resolution