Hi all! I've been lurking these forums for years, and I finally have to post something to find what I need

My old computer is broken, so I want to build my own for the first time to play World of Warcraft: MoP, StarCraft 2: HotS,Diablo 3, DotA 2, and League of Legends. I don't play first person shooters, may try a F2P one or something but not my cup of tea. I'd like to play those 4 games on Ultra if possible. I'm use to running WoW on Med-ish settings with a 5-10 FPS, and before it crashed I could no longer raid 25-mans. I don't do anything else with my computer besides run Pandora when I clean my apartment or watch YouTube. Though, if it's nice enough I might start getting games on Steam.

Here we go!

•Budget: I'd like to keep it under $821 USD for parts, that way, when I get the $99 OS plus tax I can keep the grand total under $1,000
•Resolution: 1280x960
•Games / Settings Desired: WoW: MoP, SC2: HotS, D3, DotA 2, LoL
•Any other intensive software or special things you do (Frequent video encoding, 3D modeling, etc): Nothing!
•Country: USA, been looking at Newegg
•Parts that can be reused: I have an old, but it does work, DVD read/re-writter, I can just swap that out if need be right?
•Do you need an OS? I DO! I am getting Windows 7 64-bit for $99
•Do you need peripherals (e.g. monitor, mouse, keyboard, speakers, etc)? I do not, but may change my mind much later.


Here are the parts I'm eyeing and why (I'm not 100% sure they all go together either...):

Case:
newegg.com/Product/Product.aspx?Item=N82E16811119233
COOLER MASTER HAF 912 RC-912-KKN1 Black SECC/ ABS Plastic ATX Mid Tower Computer CaseModel #:RC-912-KKN1 $59.99
Seems basic, nice air flow, and lots of room for a newb like me to build with?


Motherboard:
newegg.com/Product/Product.aspx?Item=N82E16813128546
GIGABYTE GA-Z77X-D3H LGA 1155 Intel Z77 HDMI SATA 6Gb/s USB 3.0 ATX Intel MotherboardModel #:GA-Z77X-D3H $129.99
This one I see recomended for a newb like me, but I heard about a cheaper one too, the:
newegg.com/Product/Product.aspx?Item=N82E16813157296
ASRock Z77 Pro4 LGA 1155 Intel Z77 HDMI SATA 6Gb/s USB 3.0 ATX Intel MotherboardModel #:Z77 Pro4 $109.99
Don't know why I'd choose one over the other.

Processor:
newegg.com/Product/Product.aspx?Item=N82E16819115233
Intel Core i5-3570 Ivy Bridge 3.4GHz (3.8GHz Turbo Boost) LGA 1155 77W Quad-Core Desktop Processor Intel HD Graphics 2500 ...Model #:BX80637i53570 $199.99
The reason I am going with this instead of the 3570k, is it's on sale and has a promo code, helping it fit into my budget, I've never OC'd before, and for the games I'm running... do I REALLY need to??

Graphics:
newegg.com/Product/Product.aspx?Item=N82E16814150515
XFX Double D HD-685X-ZDFC Radeon HD 6850 1GB 256-bit DDR5 PCI Express 2.1 x16 HDCP Ready CrossFireX Support Video Card with ...Model #:HD-685X-ZDFC $149.99
This has been a tough choice, trying not to get something more than I need but I also don't want to ruin myself either! Plus the price to fit my budget... is this still worthy?

Power Supply:
newegg.com/Product/Product.aspx?Item=N82E16817341018
OCZ ModXStream Pro 700W Modular High Performance Power Supply compatible with Intel Sandybridge Core i3 i5 i7 and AMD Phenom $89.99
Is this a good one and enough (W)? I've seen some say 500W is fine, but if you go to like iBuyPower they MAKE you get at least an 800W with some builds....

RAM:
newegg.com/Product/Product.aspx?Item=N82E16820231428
G.SKILL Ripjaws X Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model F3-12800CL9D-8GBXL Model #:F3-12800CL9D-8GBXL $38.99
I chose these since the promo code puts them below other choices at full price.

HDD:
newegg.com/Product/Product.aspx?Item=N82E16822136533
Western Digital Caviar Black WD1002FAEX 1TB 7200 RPM SATA 6.0Gb/s 3.5" Internal Hard Drive -Bare DriveModel #:WD1002FAEX $109.99
Now, why would I choose this one over this?
newegg.com/Product/Product.aspx?Item=N82E16822148764
Seagate Barracuda Green ST1000DL002 1TB 5900 RPM SATA 3.0Gb/s 3.5" Internal Bare Drive -Bare DriveModel #:ST1000DL002 $69.99

DVD:
newegg.com/Product/Product.aspx?Item=N82E16827118067
Sony Optiarc 24X DVD Burner, Bulk Package Black SATA Model AD-7280S-0B - OEMModel #:AD-7280S-0B $17.99
Also like I said, if I'm getting in close, and can put that $18 elsewhere, I think I can just rip it off my other computer

OS:
newegg.com/Product/Product.aspx?Item=N82E16832116986
Microsoft Windows 7 Home Premium SP1 64-bit - OEM $99.99
This actually worries me... I just found out what OEM means... am I going to be able to install and use and upgrade this on my own without any issues? Or do I need to now spend an extra $80 for the other one:
newegg.com/Product/Product.aspx?Item=N82E16832116716

Heatsink:
newegg.com/Product/Product.aspx?Item=N82E16835103099
COOLER MASTER Hyper 212 EVO RR-212E-20PK-R2 Continuous Direct Contact 120mm Sleeve CPU Cooler Compatible with latest Intel ...Model #:RR-212E-20PK-R2 $34.99
I see this recomended and all, but will I really need it for what I want to do with no OCing (Unless your telling me elsewise!)? If not, this plus the DVD R/RW can free up $52.98 getting me closer to other parts or getting that OTHER Windows 7?

Oh and THANK YOU SO MUCH for your help. I pay attention to detail and never done this before, so I have losts sleep over trying to build this thing for under $1000! (Well, $920 including Win7 OEM...)