500w or 550w PSU for my computer?

yoosuf290

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Dec 7, 2011
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My specs (Dell Optiplex 755 MT):

Intel Core2Quad Q6600
8GB DDR2 RAM (4x2GB)
2 7200RPM Hard Drives
1 DVD/RW
PCI-E USB 3.0 Adapter (May connect many USB 3.0 drives and peripherals!)
PCI 300Mbps Wireless Card
SAPPHIRE 100-505844 AMD FIREPRO V4900 PCIE 1GB Video Card (450W recommended!)
(Around) 7 USB 2.0 Accessories

So should I get a 500W PSU or 550W PSU?

If 500W, I'm going to get the EVGA 500w 80PLUS Bronze.
if 550W, I'm going to get the XFX Pro/TS 550W 80PLUS Bronze.

Which one is better? How much power does my system would use? I like the EVGA 500W but is it enough for my computer?