Mid Range Design and Gaming Build

Processor: Intel Core 2 Quad Q6600
Motherboard: MSI P35 Neo2-FR Intel P35 CrossFire Chipset
Memory: Corsair XMS2 w/Heat Spreader 2x2GB
Graphics Card: ATI Radeon HD 4850
Cooling: ASUS Silent Knight II CPU Cooler
HDD: 500GB SATA-II 3.0Gb/s 16MB Cache 7200RPM HDD
Sound: On Board
Case: NZXT Lexa Blackline Performance Mid Tower Steel 420W with maximum fans
Power Supply: Hiper 630W Type-M SLI/CrossFire Ready Power Supply
OS: Vista Home Premium 64-bit

This is ideally for my design work (Photoshop and 3D CAD) at university (studying 2nd year of architecture.) Still, I can't design my love of gaming and thus it is to supply me with a decent gaming rig. Currently the parts I am particularly unsure on are the Motherboard and Power Supply.

I had considered taking the 4870 instead of the 4850 but for £60 it hardly seems worth it seeing as I have already broken the budget of £800 (this spec clocks in at £880.) Also, I have chosen Crossfire compatible hardware so I have the option of adding an additional 4850, or upgrading to the 4870x2 when released.

As far as Overclocking goes, im currently inclined to say I wouldn't simply because its an unknown beast to me! However, its possible that I would indulge at a later date.

Any help would be much appreciated.

(Excuse any technical fo-parrs  )

Sam.