Why a 680i but no SLI???? Thats the whole fricking point of paying so much for a 680i!! if you weren't going to actually go SLI you would want something like a DS3, Abit AB9 pro, P5B-E, or P5B-Deluxe.
Your misunderstand once again. Just because the wattage of a Power supply is higher doesn't means it runs that much all the time A Power supply will only supply as much power as your system requires.
Most power supplies are advertised as maximum output. For example lets say a noname 600 watter is advertised. This means you can peak at 600 watts Under heavy load, while it may only be able to supply 500 or 550 watts continious. Other more reliable brands advertise the wattage as continious and not peak. For example a 750 watt PC Power and cooling may peak in the 800 or even 850 watt range. But they are advertising 750 watts continious meaning, that this power supply can supply 750 watts reguardless of load.
Don't confuse that with use all the time. Just because its rated at said wattage for continious doesn't mean it is always putting out 750 watts.
Knowing the continious wattage of a power supply is better than going off of and knowing its peak.