Not quite. Almost all of these cards seem to come with a factory OC to varying degrees for some reason. Only 3 of the 12 1gb GTX 460s on Newegg are actually sold at the default speed of 675mhz. The factory OCs are meaningless of course as you can easily OC the cards on your own and to better effect but as sold they do indeed have different performance levels.
Yes it should be, as long as its not some cheap unit that came with the case. Do you know the make and model ?
Yes, it's an Antec (EarthWatts). Not a cheap unit that came with the case