You can ease the control of LEDs and reduce the flickering, when you use serial shift registers with output latch, so that you can actualize next column, while actual column is still driven by latched output
not 'can' but 'must'

Since you, based on the schematic I see in
http://www.8052.com/forum/read.phtml?id=73681
use multiplexing, you must run your multiplexing at a mimimum of 1kHz to avoid flicker giving you 1 millisecond to update the shiftregister contents. Make sure you can do that also after expanding the sign (as I think you mentioned). One way to achieve that is to use more than one 'string of shiftregisters'.
I have seen more flicker during the development of our signs than I ever wnat to see. REMEMBER: most people can see flicker at a 100HZ update rate, a few can see it at 120Hz.

Erik