Rig:
Chassis: Antec 900  
Power Supply: 750W Corsair HX (Dual SLI Compatible) (Silent Edition)  
Processor: Intel Core 2 Quad Q9450 2.66GHz (1333MHz FSB) (12MB Cache)  
Motherboard: Asus Rampage Formula (Chipset: Intel X48) (Supports CrossFire)  
System Memory: 4GB DDR2 Corsair at 800MHz Dominator DHX (High-Performance)  
Hard Drive 1: 500GB Western Digital (16MB Cache) (7200 RPM) (SATA)  
Optical Drive 1: DVD-ROM/CD-ROM (DVD Reader 16x / CD Reader 40x)
Internet Access: D-Link Wireless-G 108Mbps (Supports 802.11g/b)  
Video Card: ATI Radeon HD 4870 512MB  
Sound Card: Integrated Motherboard Audio
Extreme Cooling: Air Cooled Stage 3 WindTunnel (Copper Heatpipe Heatsink & Additional Case Fans)  
Internal Lighting: Blizzard Internal Lighting (Blue Edition) (Cold Cathode Tubes)  
Windows OS: Microsoft Windows Vista Home Premium (64-Bit Edition)  
Office: Microsoft Office 2007 Basic (Word Excel Outlook)  
Speakers: Logitech 2.1 System (Includes Subwoofer)  
Warranty: 3 Year Platinum Care Extended Parts & Labor Warranty
 
If I was getting an online integrator (I'm thinking digital storm) to make this PC for me, and they have a three year parts and labor warranty, good customer service etc..., how much do you think is a reasonable price for the above computer? And what good price / performance changes would you make? And would I need a more powerful PSU if I was ever thinking about getting another 4870 and crossfiring?
 
Thanks