Final Gaming PC Build Checks - Opinions/Help

Currently in the last stages of completing my Gaming PC search. Before I go ahead, I would like any valid opinions or help on each part and the overall build.

SPECIFICATIONS:

-CASE: Corsair Obsidian Series 650d
LINKS: http://www.amazon.com/Corsair-Obsidian-Series-Computer-CC650DW-1/dp/B004UE1W9K
http://www.corsair.com/en/power-supply-units/cx-series-psu/cx-series-cx750m-modular-atx-power-supply-750-watt-80-plus-bronze-certified-modular-psu.html
WHY? Great for Cable management, good cooling built in and great build quality.

-PSU: Corsair CX Series 750W Modular
LINKS: http://www.amazon.com/Corsair-Series-Modular-Bronze-CX750M/dp/B00ALK3KEM
http://www.corsair.com/en/pc-cases/obsidian-series-pc-case/obsidian-series-650d.html
WHY? For the future basically. The 80+ Bronze is also reassuring of the great quality of Corsairs products.

-CPU: Intel Core i5 3570k Quad Core 3.5GHz
LINKS: http://www.amazon.com/Intel-Core-i5-3570K-Quad-Core-Processor/dp/B007SZ0E1K
http://www.intel.com.au/content/www/au/en/processors/core/core-i5-processor.html
WHY? $100 cheaper than the i7 which is the same as the i5, except quicker when doing CPU intensive things. For Gaming, great and Intel makes good products.

-MOTHERBOARD: ASUS P8Z77-V PRO
LINKS: http://www.amazon.com/ASUS-P8Z77-V-PRO-Intel-Motherboard/dp/B007G51UV0
http://www.asus.co.nz/Motherboards/Intel_Socket_1155/P8Z77V_PRO/#specifications
WHY? Supports Nvidia Quad SLI & AMD QUAD CROSSFIRE.
HELP: If it says it supports QUAD CROSSFIRE, or QUAD SLI, does it mean up to QUAD, or Only QUAD when more than 1 GPU?

-RAM: Corsair Vengence 8GB (2x4GB) Dual Channel Memory 1600MHz
LINKS: http://www.amazon.com/Corsair-Vengeance-240-Pin-Platforms-CMZ8GX3M2A1600C9/dp/B004CRSM4I
http://www.corsair.com/memory-by-product-family/vengeance/vengeance-8gb-dual-channel-ddr3-memory-kit-cmz8gx3m2a1600c9.html
WHY? Apparently 8GB is good when playing games, and nothing more is really needed.

STORAGE
-SSD: Samsung 840 Series 120GB
-HDD: Seagate Barracuda 2TB
LINKS: http://www.amazon.com/Samsung-Series-120GB-internal-MZ-7TD120BW/dp/B009NHAF06
http://www.samsung.com/us/computer/memory-storage/MZ-7TD120BW
http://www.amazon.com/Seagate-Barracuda-3-5-Inch-Internal-ST2000DM001/dp/B005T3GRN2
http://www.seagate.com/internal-hard-drives/desktop-hard-drives/desktop-hdd/
WHY? using the combo of an SSD & HDD, it allows for fast OS, programs and bulk data, e.g. Photo's & Document, to be stored on a large HDD.

-VIDEO CARD: Gigabyte AMD Radeon HD 7970 3GB GDDR5
OR
Gigabyte Nvidia GTX 680 4GB GDDR5
LINKS: http://www.amazon.com/Gigabyte-Radeon-Mini-Displayport-Graphics-GV-R797OC-3GD/dp/B00752QYLK
http://www.gigabyte.co.nz/products/product-page.aspx?pid=4102#ov
http://www.amazon.com/Gigabyte-Displayport-PCI-Express-Graphics-GV-N680OC-4GD/dp/B009LTUC9A
http://www.gigabyte.co.nz/products/product-page.aspx?pid=4373#ov
WHY? Original choice was the Nvidia GTX 670, but with the 7970, there is 20% performance increase apparently, and is only $40 more than the GTX 670. And if I ever happen to find myself using something that's got loads of textures, the 7970 has +1GB over the GTX 670. *UPDATE*: Have founf GTX 680 only +$70 more than the 7970. Need help choosing which is better.
HELP: Unsure which is better, AMD 7970 vs GTX 680. have looked every where, and have not found the best for PERFORMANCE, not PRICE.

-OPTICAL DRIVE: Lite-On Super AllWrite 24X SATA DVD+/-RW Dual Layer Drive
LINKS: http://www.amazon.com/Lite-On-Super-AllWrite-Layer-Drive/dp/B002YIG9AQ
http://www.liteonit.eu/en/optical-storage-dvd-rw-internal/ihas124-04.html
WHY? Good bang for my buck! Pretty cheep, and good for whenever I may have to use it.

Questions:
-For the motherboard, it says in the specifications it supports QUAD CROSSFIRE, or QUAD SLI, does it mean up to QUAD, or Only QUAD when more than 1 GPU?
-Unsure which is better, AMD 7970 vs GTX 680. have looked every where, and have not found the best for PERFORMANCE, not PRICE.

Any Support and opinions much Appreciated.