Help On New System

Well since summer is coming, I am planning of building myself a new system, since my current one is dying on me. This is the second one I'm making, so I am a bit frail towards hardware experience.

The system use is hanging between editing, specially Photoshop, and playing Games. My budget ranges at around 1000 to 1500 dollars. I only need the system, the optional stuff arent necessary

I will probably Overclock my Processor whenever the time is right, if that can help.

I currently chose to buy those at the moment:

MB:ASUS P5Q Pro Motherboard
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
130$

Processor:Intel Core 2 Quad Q6600 Processor 2.4 ghz
http://www.ncix.com/products/?sku=22211&vpn=BX80562Q660...
300$

Memory: OCZ Platinum OCZ3P16004GK 4GB DDR3
http://www.ncix.com/products/?sku=30371&vpn=OCZ3P16004G...
80$

GPU:Sapphire Radeon HD 4850 X2 1GB
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
220$

Case:Antec Nine Hundred Mid Tower Gamer Case
http://www.ncix.com/products/index.php?sku=21123&vpn=NI...
150$

PSU:Antec Earthwatts 750W Power Supply ATX12V
http://www.ncix.com/products/index.php?sku=38107&vpn=EA...
140$

Extra Fan:Noctua NF-P12-1300 120MM Ultra Quiet Cooling Fan
http://www.ncix.com/products/index.php?sku=27129&vpn=NF...
20$

HDD:Western Digital Caviar Blue 320GB SATA2
http://www.ncix.com/products/index.php?sku=39193&vpn=WD...
65$

Total:~1100$


1.Any advice on what I should change in my build?

2.Is a Quad Core too much for what I need(editing and gaming)?

3.I'm not so comfortable using an ATI Graphic Card, I always had some misadventure with them. Is the 4850 X2 reliable on running graphics?

4. Is the cooling enough in the system? And is a 750W PSU more than necessary.

I appreciate for the help.