|What I hear the OP saying is that he is willing to pay $100 more for 25% increase in performance. |
550W power supply means next to nothing. You need to look at Wattage. The chart Mick linked shows the draw for both. Divide those numbers by 12 to determine how many amps each one will draw. That comes to 14+A & 18+A just for graphics. Depending on what CPU you are running that could add another 140W. Then of course there are motherboard needs, drives & fans.
A quality 550W unit may supply that, but a cheap $20 unit probably won't.
You may need a power supply with a single 12V rail with at least 34A.
Below is a link that may help you with the pricing.