What do you think of this system?

I would recommend going for the gtx 590, just because nvidia usually has better drivers than AMD, in my experience. Overall, the system looks really good. I completely agree that the 980x is complete overkill. Unless you're loaded with cash and just want to burn money in order to have the absolute best system that money can buy, It's pretty pointless. As for the sound difference between the two video cards, the 590 will be quieter than the 6990. According to the guru3d review, the gtx 590 gets up to 41 decibels under load and the 6990 gets up to 47. As for DVD drive, I personally just went with http://www.newegg.com/Product/Product.aspx?Item=N82E168.... I have had absolutely no problems with it and it writes DVDs fairly quickly. Also, it isn't very expensive.

Just some general ideas that you could consider:
Instead of the motherboard that you have listed now, you could also consider the asus p6x58d premium. I've had very good experiences with this motherboard and it allows easy overclocking. I managed to get my core i7 930 up to 4.2 ghz without any issues. It would be a little cheaper than the motherboard that you are currently looking at and would work with the specs that you've listed. The only issue with the motherboard is that unless you have a EXTENDED CASE, you will not be able to fit more than two video cards in your case when using this motherboard. Unless you are using three video cards, this is not an issue, however. Like the motherboard that you were considering, the asus has USB 3.0. Here's the link: http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Overall, good looking build. Let us know how it goes!

I would not go with the GTX 590. it has overheating problems when overclocking. if you go onto videocarkbenchmarks.net and look at the high end video card chart. the GTX 580 still holds the top spot. and its 200 cheaper. they blew 5 590s doing overclocking tests
approximately how much is this build altogether. i could put together a build for you thats the same price thats just as good.
and if you are just going to be using this for gaming. The i5 2500k is $100 cheaper and will handle any game you throw at it. The hyperthreading technology in the i7 2600k is only if your doing video and model editing in my opinion. i5 will fit all your needs

What kind of things are you going to be using this for?
PS. on newegg.com the 6990 is same price
your not only missing a DVD drive. if you want gaming performance getting into overclocking is fun. i recommend the cooler master hyper 212+ with an extra fan so you get a push pull effect on airflow for the CPU cooler