No trouble and atleast your FPS have improved with the newer card
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When looking at power supplies if possible try to get something with an 80% efficiency. That way you will have a PSU that is more stable and constant. Also its a good idea to check the +12V rails and see what output they produce. As different PSU put out different levels. Of course the higher the output on the rail the better the power supply will be at powering devices such as video cards.
I wanted to double check and make sure you would get a card that suited your motherboard. As you wouldn't believe the amount of people who have made mistakes by buying a video card that doesn't suit the slot on their motherboard.
I have even seen some brand name computers have the same specs and exactly the same hardware inside them bar the video slot. I have seen some with the older AGP slot and others with the PCI Express slot. Bizarre I know! But all to true.
Anyway I hope it all works out for you and you are finally able to enjoy the game. If you any other queries just let me know and I will try to help you where I can.
PS: Here is a link in which you can compare video cards. You can select different benchmarks from the drop down box and compare different games with different settings etc.
http://tinyurl.com/ybju66e
Although it does not list the 4650 it lists the 4670 so it will give you a close guide as to how your card performs with others.