the 650 is more powerful - and I've literally chosen that.
I'm getting mine in 2 days.
There are 650's without PCI-E power connectors, such as the ASUS GTX650-E-1GD5, but I have purchased a PSU that has that connector, and can easily handle a 650, and I'd rather get the one that requires that connector, to have overclocking potential later on.
I wouldn't get a 650 on a cheap local power supply though. The power supplies literally suffocate graphics cards(even my Geforce 210 was bottlenecked; and it requires only 31W. I had an Odyssey power supply BTW, and now I got a Corsair CX430).