In general the 6790 is a graphics card to avoid . Its a chip with errors , so they just enable parts of it so its saleable. Its fine for lower resolution screens I guess.
I would spend th money you save by not getting all that RAM on a 6850
As you said you spend a lot of money on certain parts. SLI or Crossfire for me isn't worth, because by the time you'll want to add a second GPU, better single card solutions will be there for you. Plus you won't mess with drivers, scaling, temperatures, power-hungry PSUs etc. Your motherboard will have this option though..
So here's a more balanced build
If you don't want to overclock i5 2400 is the way to go. Otherwise you must look at 2500K
I'd be cautious buying a video card right now as rumors persist about possible Radeon 7XXX-series cards in Q4. Even if they are simply 'mid-range' they will drive prices down. If you feel you need to jump, the dual-BIOS Sapphire Radeon HD 6950 Dirt3 Edition 2GB is $253 after rebate and a BIOS-flash away from an HD6970.