I use quite a lot of peak current with IR LEDs, you can pulse some at 1 amp, in some TV remotes they dont even have a resistor in series, but use the internal resiastance of the battery to limit the current.
But if I can only drive my LEDs at 150Ma, and its only for 1/8th of the time, it would be about the same " power" being supplied to the LED as driving it at 18mA DC.
So what I was trying to find out ( as I havn't actually looked into multiplexing before ) is that if I have all 800 LEDs on at once, and I want them the same brightness as if they were all on at 18mA, would I need 8 rows and 100 columns with 100 LEDs on at once ?