The i7 and the HD5870 completely trash their counterparts in the AMD build. I would say wait for the 3.2GHz Black Box Thuban, but unless you do a lot of rendering or something, the $310 Thuban is unjustifiable since the i7 grants you better performance in games and in audio/video encoding/decoding. The HD5870 is also a huge step up over the GTX260 Core 216. If you want to save money, go with the HD5850, 5770, or GTX470.

The flip side is that the AM3 socket can be upgraded with any new AMD processor for the foreseeable future, requiring only a BIOS update and the appropriate TDP tolerances. A good compromise would be to take that AMD system as is, but remove the GTX260 give it an HD5850 or HD5870. You save money and maintain more than adequate gaming performance. Remember, most games are GPU-bound, not CPU.