isn't a good idea to have a little "head-room"?
by brother has a band and says that his amps are bigger than he NEEDS but with the extra "head-room", it makes for cleaner sound.
yea or nea?
Audio requirements can vary dramatically (and to be honest, live amps tend to be very noisey). Deep Bass can quickly eat up all your power.
For the most part your system is going to use what it's going to use.
Take a look at reviews of systems with 8800GTX SLIed, and you'll find they generally use under 500 watts. The only exception that I can find to this is Hard OCP's BFG review (which doesn't actually review in in SLI, but we can extrapolate from other reviews that the 8800gtx uses about 155w).
But even that's misleading, because with the exception of the 155w figure, almost all PSU measurements are measured at the wall. If you assume a decent efficient PSU was used, then you take the measured wattage * .80.
Even if it's 600w, you're actual usage is 480w. What these other sites can't account for is how much power your drives use. If these were WD RE drives, they probalby use under 1amp each (around 9 watts). OTOH, Seagate seems to suggest that the 7200.10 use a whopping 2.8a (which is shockingly high, but that's probably only at start up, which can be overcome by staggering when the drives spin up).
Bottom line is that Mpilch has already got plenty of headroom in the PSU size he suggested.
Enjoy your rig.....I dn't envy the price you paid for those cards, but I do envy the performance