i would choose the hd 6870 over the gtx 470..... the gtx 470 runs hot and draws a lot of power, the hd 6870 does not run hot at all and does not draw a lot of power,also ATIs crossfire scaling has improved dramatically 2x hd 6850s in crossfire beat 2x hd 5870s in crossfire (bear in mind ATI changed their naming scheme so the hd6850 is actually the replacement for the hd 5750) now just imagine what the hd 6870 can do in crossfire? could you wait though? with intels new cpus coming around the corner and the rest of the ATI 6xxx series and the gtx 5xx series around the corner i really think its worth the wait
If I were you, and in a way I am, (doing the same line of work and building a new computer) I would go with a new Power supply unit. I went through the effort of looking for you and this PSU is a failure. Never try to save money by feeding your components unreliable, crap energy and thats what this PSU has been proven to do. My XPS was a total loss by a PSU failure, everything was possibly damaged. (Apparently, Dell likes cutting corners with cheap PSUs.) Anyway, see the link below if you are concerned about keeping your Beast healthy.
Even if you don't know what ripple is, I think you might get the point. So, for all reasons above, I'd advise using Corsair, they have a record for minimal ripple and offer great power efficiency. And secure your PSU/computer from electrical noise and instant damage by using a UPS.. I learned by error.
Anyway, I'd prefer 3x4Gb 1600 RAM. By all means 6 gigs are great for gaming, plus with the extra cash you save with 2gig modules you can buy top notch ram or a number of other things. But it may cause bottlenecks for an OC system with a demanding user.
You must be aware that the OS always claims a significant portion of what you install. IE, 6 gigs could only be 4.5gigs available in some setups. Anyway, you may think 12gigs (3x4gb) is too much, but if you plan to use SLI, especially in PCIe 16x, a significant portion of that 12gigs of ram should be happily utilized, and you will be good for many years.
Yeah, decent choices, minus the otherwise previously stated PSU. I'd change that.