Warmagoo, I just built that exact system, but after having the 690 for a week or so, I traded it to a friend who really REALLY wanted it and they were out of stock then, and bought myself 2 680 ftw+LE 4gb and sli'd them.
The system you have, particularly the video card, it's just begging to be run on those 3 monitors. You won't find a better solution for running 3 screens for gaming out there unless you get into the ridiculously priced CPU's that are over 1000$ and uber 4000$ video cards. You just can't. The 3930k I'm running is o/c as well, but to a bit higher ghz than yours, but it'll be close enough for horseshoes and hand grenades. The 690 is essentially a dual GPU solution on one card, and performs very very similarly to my 680 sli cards - within single digits percentage wise on most apps/games in my personal experience. You don't need any additional equipment like you do with some of the eyefinity setups depending on your monitors and if they are display port capable etc. You should be ready to go so long as you have the various connecting cables you need to go from your GPU back plate to the 3 Dell monitors. If you're an Aces High player, prepared to be blown away by the difference you'll see not only with the settings all slammed to the max, but on all 3 screens. Performance wise, my experience is that you will likely never see less than 59/60 frames per second, even on maximum detail, over 3 cv's firing the much loved puffy ack, and with 20+ red guys flying around. Also, quick edit, but running triple monitor is a more enjoyable and better way to go than a big screen TV IMO. I tried my system on my 60" LED 120hz tv, and it wasn't as good as running my 3 monitor setup, at least to me.
Just a quick off topic question, but what is the cooling method you're using for your 3930k? Even with a middle of the road cooler you can very likely clock it a fair bit faster and still see relatively low temperatures for a 24/7 overclock. If you're using one of the easy peasy water coolers from Corsair or cooler master, you can push that 3930k up another 10% or even higher with the same level of risk and heat that you're currently having at 4.2. Just food for thought, have a read through overclocker BBS's about the 3930k. It's really an excellent overclocking little chip.
