First of all the motherboard is ok, but I would go with a Gigabyte board, for price and overclocking. That may not interest you now but it may in the future. Gigabytes P35 and P45 series are solid any of those with DS3 or DS4 in the model number will suit you well.
Also unless you are a huge sound enthusists I would go with onboard sound.
You won't need 850 watts for your video card. Espeically with a board you can't SLI with. I suggest a solid 650 watt Antec is a good brand, PC Power and Cooling is great, Apvia is ok, Hyper is Good. For a gaming PC a Core 2 Quad is overkill and that one is way overkill.
Generally I would say don't skimp on the CPU but really the price difference I would say get a Q6600.
Finally I wouldn't get a high end GPU from nVidia right now. The GTX260+ is ok however I'm thinking we may run into a Geforce 6800 vs Raedon x800. The x800 could do about everything the 6800 could however without SM 3.0 support the x800 fell out of the gaming circle really fast. I think the rolls may be reversed this time. I would go for a HD 4870 at the moment.