The recommended total Power Supply Wattage gives you a general idea on what to look for BUT it is NOT a crucial factor in power supply selection! Total Amperage Available on the +12V Rail(s) is the most important, followed by the +5V amperage and then the +3.3V amperage.
GPU's draw power from the +12V rail and cheap PSU's often/sometimes don't have that much on the +12V so if you have a "cheap" (not always so easy to know) model you might want to take that into consideration.
PSU's degrade after time. I believe it is around 5-10% loss per year and quality of the PSU most likely affect this too. They can also not run on max power for any long periods so the bigger buffer you have the better in the long run.
Also, you will not get a linear 100% boost in most games from SLI, atleast not from what I have read. But that was some time ago so you might want to read up on that. Newer single cards draw less power but are still more powerful then older SLI cards.
Maybe take a look on Tomshardware.com 's GPU charts and see if you can find a card thats faster then 2 8600GT cards and see if you can buy that instead.
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GPU's draw power from the +12V rail and cheap PSU's often/sometimes don't have that much on the +12V so if you have a "cheap" (not always so easy to know) model you might want to take that into consideration.
PSU's degrade after time. I believe it is around 5-10% loss per year and quality of the PSU most likely affect this too. They can also not run on max power for any long periods so the bigger buffer you have the better in the long run.
Also, you will not get a linear 100% boost in most games from SLI, atleast not from what I have read. But that was some time ago so you might want to read up on that. Newer single cards draw less power but are still more powerful then older SLI cards.
Maybe take a look on Tomshardware.com 's GPU charts and see if you can find a card thats faster then 2 8600GT cards and see if you can buy that instead.