The good news is that all your suspicions were correct, the 7900GTO is indeed a re-badged 7900GTX which means you're getting amazing bang for your buck on these cards with the rates they're selling at! 
The bad news is that it's not just a re-badged 7900GTX, it's a re-badged 7900GTX from the older batches with faulty memory and/or voltage regulators and has had the memory down-clocked to cope!
Reports are coming in that these cards are failing rapidly, especially when the memory is overclocked, and that some people have even noticed that their cards can only be refurbished and not new.
Here are links to the thread on the official EVGA message board and the original thread at XS.

The bad news is that it's not just a re-badged 7900GTX, it's a re-badged 7900GTX from the older batches with faulty memory and/or voltage regulators and has had the memory down-clocked to cope!

Reports are coming in that these cards are failing rapidly, especially when the memory is overclocked, and that some people have even noticed that their cards can only be refurbished and not new.
Here are links to the thread on the official EVGA message board and the original thread at XS.