For testing PSUs with a bit of a hefty wattage we like to put every piece of hardware we have together to mimic the most powerful of PCs that some of you will have. So we put together these two PCs:
Intel Core 2 Duo E6600
Asus P5W-DH Deluxe
2 x X1950 PRO (Crossfire)
OCZ 2GB PC6400 5-5-5-15
AMD Athlon X2 3800+
eVGA 8800 Ultra
OCZ 2GB Special Ops. PC6400 5-5-5-15
The Corsair then powered not only the master PC, but it also fed both 6pin slots on the 8800 Ultra and about 4 HDDs and 6 120mm fans not including the CPU coolers; oh, and each PC had a molex powered PhysX card in too :).
Using Asus Probe and a multimeter for confirmation, we recorded the voltages of the rails over a 30 minute period with everything at idle and then loaded every component we could and repeated the result taking.