Where did you get that the P5K is SLI-ready???
Get a P5N-D if you want the ability to add a second 8800GT later in SLI. Your 700W GameXStream and the Antec 900 are good for that already.
Apart from that, all good.
Get an E8400 if you can stretch the budget a bit. If you can also afford a HDT-S1283 cooler for overclocking that would be even better.