I've also been considering getting the 790i if DDR3 prices drop a bit by the time it comes out. I think when it does come out, ddr3 prices will drop due to nvidia and intel then having ddr3 capable boards. From what I've heard its been slightly delayed as nvidia didn't want to release it so soon after the 780i but I think its on course for somewhere in march, I'm guessing just after the 9800gx2.
As for 780i vs striker 2 formula. I have an nvidia chipset simply because i prefer them and I like to have the option to run SLI if I want to. If you don't plan on running SLI then the striker 2 formula is an excellent board but the customer support, warranty and step up programs at Evga are fantastic. If I was in your position, it would come down to SLI for me. Also remember than the 780i is only marginally different from the 680i.