~1100 Gaming Pc (advice)

Approximate Purchase Date: Between now and Black Friday

Budget Range: Around $1100

System Usage from Most to Least Important: Deep Fritz 12 (chess engine), Gaming(Fallout3, eventually Diablo3)

Parts Not Required: Monitor, 2.1 Speakers

Preferred Website(s) for Parts: amazon.com (free shipping with prime), microcenter.com, newegg.com

Country of Origin: US

Overclocking: No

SLI or Crossfire: No

Monitor Resolution: 1650x1080

Additional Comments: I don't plan to overclock, and I really don't expect to upgrade before this current gen of technology is obsolete. I will probably upgrade to a nicer monitor at some point, but that might be it. Also I'm a newbie to building.

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For the processor I was thinking i-7 870 for $230
http://www.microcenter.com/single_product_results.phtml...

GPU Radeon5850 for $~300
(I don't know which version to get, would appreciate input)

Mobo - Gigabyte GA-P55M - UD2 Ultra Durable 3 Motherboard $105
http://www.amazon.com/Gigabyte-GA-P55M-Ultra-Durable-Mo...

HD 1- Intel 80 GB X25M Mainstream SATA II Solid-State Drive $194
http://www.amazon.com/Intel-Mainstream-Solid-State-Pack...
HD 2- Western Digital Caviar Black 500 gb Bulk/OEM Hard Drive 3.5 Inch, 32 MB Cach $60
http://www.amazon.com/Western-Digital-Caviar-Desktop-WD...

PSU- Corsair CMPSU-650TX 650-Watt TX Series 80 Plus Certified Power $90
http://www.amazon.com/Corsair-CMPSU-650TX-650-Watt-Cert...

Case- Antec Three Hundred Gaming Case External 3 X 5.25; Internal 6 X 3.5 2*Usb2.0 $60
http://www.amazon.com/Antec-Three-Hundred-External-Inte...

Memory - CORSAIR XMS3 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) $88
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Total----------------------------$1127
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A few questions.

Is the current selection for Mobo's mATX size going to complicate anything?

Do I need a sound card, or is onboard sound good enough? (I don't record or have expensive speakers)

I'm not planning on OC'ing, should I get a cpu cooler or extra fans anyway, for longevity?

Should I buy anything at the moment (like the microcenter processor steals) or just wait for the possible sales (radeon 5850?); or both.

And obviously; please let me know what's a mistake or something that you would do differently.

Here is a comparison on CPU for chess engines http://www.tomshardware.co.uk/charts/2009-desktop-cpu-c...