I would suggest a better PSU, such as a 550W-650W XFX. The Corsair "CX" line is made with some inferior Samxon capacitors that cannot take heat and have been cited for early failure.
As to your question though, I'd get a dual-band PCIe x1 adapter. They aren't the cheapest, but the performance difference will absolutely be worth it, especially if you will play games over a wireless connection. Cheap adapters tend to have poor antennas and weak radios.
The best thing to do (assuming an ethernet cable straight to router is not an option) is to use a powerline network adapter over wireless. A good 500mbps adapter will cost about $40 but will provide you with significantly better ping times then wireless, and in gaming it is ping/latency that maters more then mbps.
This will be better then any wireless card. pci-e cards are better then usb if you are just dead set on using wireless. The usb adapters are just not that good between not enough size for a good antenna and not enough juice out of the 5v usb plug.