Hey man, thats a a great set up, but i think i might have a few ideas on how to save a few bucks. First off your cpu, I would recomend a AMD FX 4100 ($110). It is a 95 watt cpu so youll save some power, its very overclockable, and its 10 dollars cheeper. Im useing one overclocked to 4.0 ghz with the stock cooler and its amazing. For what your wanting to do it would work just as great. Its still only a ten dollar difference so its up to you.
Your main problem would be your graphics card. Im not 100 percent sure that this card will run the games you want on ultra at good frame rates. What ever extra money you have should be put into the graphics because thats what your games are going to reliy on. I would suggest looking at last generation cards like radeon 68xx series or an nivida card 550 and up. It would be worth the while to look in to a radeon 6870 or a nivida 550 ti. Both should run what you want just fine.
Your power supply looks great, just make sure that it will have enough PCI Express connectors on it to support the graphics card you choose. Also depending on the power supply you get make sure its maximum wattage will support your system. A great tool is on newegg (http://images10.newegg.com/BizIntell/tool/psucalc/index.html?name=Power-Supply-Wattage-Calculator).
Your motherboard is great, but i found one with a few features you might like. ( http://www.newegg.com/Product/Product.aspx?Item=N82E16813157323 )This board comes with two sata 6 gbs ports, which means you can get a faster hard drive. It supports higher speed ram, 6 channel audio and much more. You can read about it. Going with this one will make you much happier in the long run because its very upgradeable. it supports 8 core cpus, high speed ram, usb 3, gigabit internet, and much more. The best part is youll save five dollars and get a whole lot more features.
The rest are just personal upgrades you can do. If you go with the asrock board i would pick up at least some 1600 mhz ram. You can get eight gigs from g.skill and it coats the same. Also i would try to get a bigger hard drive that has sata 6 gbs connectors. Believe me that you will fill up 250 gb in no time once you fid steam sales. If you cant get a bigger one you can always buy one later and add it in.
All in all your system is pretty good. These were just a few things that you could change to help out in the long run. You dont have to do them. Also 100 dollars seems a little high for shipping. I think the last computer i ordered was only like 30-50 dollars in shipping. So you might look into which part has the higgest shipping coast or wait for deals for free shipping or discounts. Subscribe to the newegg news letter if you havent already, It usually has great deals. 2013-01-02
In regards to which operating system i would go with windows 7 for sure. Windows 8 is still being figured out so unless your monitor is a touch monitor i would greatly advise windows 7. It will support all your games and youll be used to how everything works.
Also you didnt say anything about the case you were going to use. If you buy one remember that the case dose not boost perfomance. Just make sure what ever you choose has some what good air flow and is some what cheep. The money you save on that can be put into other parts that will make your computer all the better.