You must have little interference. I have a 300mbps kit and was getting ~2.5MB/s. Many reviews on Newegg are saying 600mbps only getting ~5MB/s.
Yeah depends on your home I guess. I had no issue getting the full speed from my fibre connection on the base ones.
I took the plunge on a Sapphire 7870 2gb Ghz after all (it was only 10 euros more than a decent 2gb 7850), but I am having thoughts on its wattage requirements..
I have a (I bet I'm gonna hear it for this) Xilence 580W, and currently it powers my mobo, a Phenom II X4 955, a 4870, 2x2 @ 1600, 2 HDDs @ 7200, an optical disc drive, a wi-fi receiver PCI card, plus, whatever USB devices I'm using (3?).
The official page of the card says it requires a 500W PSU.
I have never had any trouble with my PSU (its roughly 3 years old)
Do you think it is going to handle it? Should I risk it?
Whilst that's not a great PSU you should be fine.