I currently have a radeon HD 5750 and was thinking about getting a radeon r9 270x but have now been looking at the gtx 770 2gb version(is there a difference between 2gb and 4gb version?). My power supply is a corsair 650 watt and was wondering if i will need to buy a new power supply? I was thinking of getting a rm750watt or higher so i have enough power to upgrade motherboard, CPU etc. in the future.