Need advice on gaming computer

I am building a new gaming computer and I have a few questions / concerns. I want to play all new games at least close to the highest settings. These are the specs I'm thinking of.

CASE: NEW!!! CoolerMaster Cosmos Silent Gaming Tower Case w/ 420 Watts Power Supply (Original Color)

CPU: (Quad-Core)Intel® Core™ 2 Quad Q9300 @ 2.5GHz 1333FSB 6MB L2 Cache 64-bit
Should I get the Q9300 or the E6850? The duo has a standard 3.0ghz which is higher but quad i think would be a better choice for the future.

MOTHERBOARD: (QX9650 Support) Asus P5N-D nForce 750i SLI Chipset LGA775 FSB1333 DDR2 Mainboard
I don't know if this motherboard is good enough to run with the rest of the computer. Would the P5N32-E SLI 680i be that much better?

MEMORY: (Req.DDR2 MainBoard)4GB (4x1GB) PC6400 DDR2/800 Dual Channel Memory (Corsair or Major Brand)
Is it better to have 4x1GB or 2x2GB?

VIDEO CARD: NVIDIA GeForce 8800 GT 512MB 16X PCI Express (EVGA Powered by NVIDIA)
VIDEO CARD 2: NVIDIA GeForce 8800 GT 512MB 16X PCI Express (EVGA Powered by NVIDIA)
I am a little worried about this, would it be better to get 1GB instead of 512MB video cards. Would it make that much of a difference?

VIDEO CARD 3: NONE

LCD Monitor: NONE

HARD DRIVE: Single Hard Drive (500GB SATA-II 3.0Gb/s 16MB Cache 7200RPM HDD)

Data Hard Drive: NONE

Optical Drive: (Special Price) 20X DVD±R/±RW + CD-R/RW DRIVE DUAL LAYER (BLACK COLOR)

Optical Drive 2: 16X DVD ROM (BLACK COLOR)

SOUND: Creative Labs X-FI XtremeGamer 24-BIT PCI Sound Card

COOLING: CoolerMaster Liquid CPU Cooling System (Superior Cooling Performance + Extreme Silent at 20dBA)
I don't know whether to get this cooling or the Asetek Liquid CPU Cooling System (Extreme Cooling Performance + Extreme Silent at 20dBA).

POWER SUPPLY: CoolerMaster Unit 600 Watts eXtreme Power - SLI Supports
Enough power for this computer?

Thanks for your input!

Buy the case without a power supply. Why pay for a PSU and throw it away. Without PSU it's $210 at Newegg.

Get a Q6700. It will beat both the Q9300 and the E6850 if you overclock it a bit. It will beat the Q6600 and Q9450 too if you do it right.

Motherboard: if you really want SLI, get the eVGA 780i
http://www.newegg.com/Product/Prod [...] 6813188024

RAM: DDR2-800 is fine. 2x2GB is better, both for easier overclocking and so you can reach 8 GB later.

Video card: get the 8800GTS 512MB, it has a better cooler and it's faster and it overclocks better.

Hard drive: for a 500GB drive, Seagate 7200.11 is a better choice than WD. For something larger, I'd prefer WD (WD6400AAKS or WD7500AAKS). For 1TB, I like Seagate more again.

Ditch the DVD ROM. Make sure the burner is SATA (easier cable management, better airflow).

I don't know about liquid cooling. It needs too much maintenance for my taste.

CoolerMaster makes good cases but their PSUs are not exactly the best. Something like the 620HX or Silencer 610W should be OK for this system, even with two video cards. If you go for liquid cooling you will probably want something bigger.