I know this is an extreme case and most people are not going to quad crossfire.Personally I wouldnt quad crossfire because I know its a waste.But people are doing it although few they may be.It recommends a 650 Watt on this model of HD 4870 X2 and for crossfire a 1 kilowatt PS.Just the manufacturers recommendation .Its nothing I made up .But I would definitely rather have too much PS than not enough.personally I think the Pc and P and Corsair 750 watts are the sweet spot right now for price/performance for handling single big cards or moderate SLI/Crossfire
http://www.newegg.com/Product/Product.aspx?Item=N82E16814161242
Brand HIS Hightech
Model H487X2F2GP
Interface
Interface PCI Express 2.0 x16
Chipset
Chipset Manufacturer ATI
GPU Radeon HD 4870 X2
Core clock 750MHz
Stream Processors 1600 (800 x 2) Stream Processing Units
Memory
Memory Clock 1800MHz
Memory Size 2GB
Memory Interface 512-bit (256-bit x 2)
Memory Type GDDR5
3D API
DirectX DirectX 10.1
OpenGL OpenGL 2.1
Ports
HDMI 1 via Adapter
DVI 2
TV-Out HDTV / S-Video Out
General
RAMDAC 400 MHz
Max Resolution 2560 x 1600
CrossFire Supported Yes
Cooler With Fan
Operating Systems Supported Windows Vista/XP/MCE
System Requirements 650 Watt or greater power supply with one 2x3-pin PCIe power connector and one 2x4-pin PCIe power connector is required (1K Watt with two 2x3-pin and two 2x4-pin connectors for ATI CrossFireX technology in dual mode)
Power Connector 6 pin / 8 pin
Dual-Link DVI Supported Yes
HDCP Ready Yes
Packaging
Package Contents H487X2F2GP
Driver Disk
User's Manual
HDTV Cable
Power Cable
DVI to VGA/D-sub Adapter
DVI to HDMI Adapter
CrossFire Bridge
S-Video to Composite Adapter
ScrewDriver
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