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Quick question regarding efficiency and 5870 Crossfire

post #1 of 6
Thread Starter 
I know a good 750W PSU will handle a 5870 crossfire just fine, but will I see better efficiency from running a quality 850w supply instead? Especially in the case that the cards are running at load 24/7?
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Home PC
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Phenom II x6 1055T (95W) Asus Crosshair IV Formula Gigabyte 5870 + HIS 5870 CF 2x 2GB OCZ Platinium DDR3 @1333Mhz (7-7-7-16) 
Hard DriveOptical DriveOSMonitor
Seagate Barracuda 500 GB TSSTCorp CDDVDW TS-H653R Arch x86_64 2x LG Flatron W2243S (3840 x 1080) 
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Seasonic X-750W Coolermaster CM690II Adv 
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post #2 of 6
I am no expert on psus, but heres what I think, if I am wrong someone else will correct me...
The more headroom left, the less amount of strain on the PSU, the less amount of heat generated, longer life of the PSU. This becomes more effective when the system is running on load nearly 24/7.
If (and only IF) this theory is correct, then get the 750 if required rating is 550watt. get the 850 if required rating is 650watt.
    
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post #3 of 6
Your best bet probably is the Seasonic x-650, even at full load(which won't be the case with 5870cf) it will be more efficient than a other 850w psu at ~50% load.
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post #4 of 6
If you see better efficiency (depending on the unit) it will most likely only be 1-3% of difference. Would make virtually no difference.
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post #5 of 6
Quote:
Originally Posted by GameBoy View Post
If you see better efficiency (depending on the unit) it will most likely only be 1-3% of difference. Would make virtually no difference.
This.
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post #6 of 6
You'd see lower efficiency. Your highest efficiency would likely be with a 650-750W, though I must comment that the efficiency curve of each power supply can vary widely.


But you would see lower efficiency with the 850W for sure. Power supplies are usually less efficient below 20% load and over 80% load, and are usually most efficient around 40-60% load. Getting an 850W PSU would mean that while running benchmarks your PSU would be very efficient, but while gaming it would be less efficient, and when just idle or browsing it would be less efficient still. Consider what you do the most.
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