I have an i5-2500 system and will be trading out my current GPU for an MSI R9 390. I have an OCZ ModXStream Pro 600W PSU that I've had for almost 4 years. On the back of the R9 box it has a minimum requirement of 750 watts for the card but says that each system may require less or more depending on components. This card doesn't draw that much power does it? Do I need more that 600 watts? Thank you.