To be honest people who run cards in SLI or Crossfire have a lot of problems. You can buy cards that are basically two GPUs in one, meaning they are already SLI, but updating drivers very often is what you will have to deal with. Also sometimes you will have to disable one card in order to get your games or programs to work properly. Dual GPU's arent really necessary. I have a single GTX 670 and it runs BF3 on high 50-60FPS whilst I'm recording. If I had a better CPU it would be a constant 60+FPS whilst recording. In my opinion dual GPUs wont be properly utilized for another few years, same as the 8 core processor. So just go for a powerful single GPU
you will save yourself money and power... And your PC will be a lot quieter!