NJ5 on 30 May 2011
I would be very surprised if the GPU was close to a HD 4650 as you suggested.
That card is basically as powerful as the 360's, and today you can buy a card like the HD 5570 for $60. That's twice as powerful as the HD 4650 and its power consumption is low enough that it wouldn't make a very hot console. A HD 4830 / 5670 with a die shrink to 32nm is also possible.
For memory I would say at the very least 1 GB.
I haven't thought much about the rest yet...
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