First let me say that you have selected some very good parts and they are high end to be sure. I certianly agree with the selections and there are some things that if you were interested in to save a few dollars to maybe use in anothe area. The GTX 680 is a beast of a card and top quality for sure but Nvidia has done something unusual in that the GTX670 is almost as good ( an avarage of 5 fps lower) and is $100 less. It almost makes no sense to get a 680 when you can get a 670 for a lot less and get the same performance. I'm still trying to figure out what Nvidia is doing .
The other thing is the 16gb of ram and you can save yourself some money there also by goping with 8gb because unless your going to be doing graphic design or video rendering then you won't be using more than 6gb of ram when gaming. I went out and got 24gb for my build figuring I would be all set with a lot of ram untill I had the resource monitor up while gaming and saw that I was only using 5 gb of ram and that's with some things open in the background as well.
So while I totally agree with your selections those are the two area's where you could save money if you wanted to.
If you chose to do that then you could take the money saved and up the power supply to 1000w SeaSonic and have enough to do any future upgrade without changing the psu. You could also add a SSD for the OS which will speed up the overall processes of the apps. It will be a lot faster then the Veloceraptor if that's what you were intending for the OS.
For SLI you need the same gpu chip so that means another 680 , It's why I was recomending the 670 since the price of the 670 is a lot less and gives almost the same performance. When you get a chance check out the article below.
The SSD that I feel is the sweet spot for using it as the OS drive is 240gb/256gb the reason being is that it will hold the OS and a few of your current games without having to constantly watch what your putting on the C drive. If you go with a 120gb/128gb or less then you have to be keeping track of what's being loaded on the C drive. I have this one and I am pretty happy with it and my second drive is the 600gb Veloceraptor.
If you're not overclocking then it's just a noise issue, stock HSFs are loud. What inzone linked would be silent at stock settings, and would also give you room to experiment with OC if you feel so inclined (do it!!!!)
If price is no object, keep the 680. I agree that the difference in performance between a 680 and a 670 are very slim compared with the price difference.
I too would swap the WD Raptor for either an Intel or Samsung SSD - they're both incredibly reliable and an individual drive will outperform even a RAID5+1 setup of Raptors. Seriously...they're rock solid and fast. I have an 120 GB Intel 520, but the max IO is slightly higher with the 180GB version. I have also used a Samsung 830 and it is a rocket as well. Pick capacity based on how many programs you currently are running and how many games you'll have simultaneously saved to the local disk. I think 180 is more than sufficient but you might have more stuff than I do.
Unless you're a media/document pack-rat, I would say 3TB is a little excessive. I have a 1.5 TB disk and have nearly 400 of my movies encoded and saved to that drive and it's not even half full.
The 850 Watt PSU should be more than sufficient to run that rig but you may have to upgrade down the road if you decide to SLI 2 680s together. They are more power efficient that the 580s, but they're still going to need some power.