skootles:
Will this display be ok to use? I believe the 90mA peak forward current means that I can safely put 40mA to it for a very short period of time, like the MAX7219 would as it cycles the digits on/off.
The 30mA is max continuous current and 90mA is a peak current when the display is multiplexed, note the "1/10 duty cycle, 0.1ms pulse width" meaning it would be on for 0.1ms then off for 0.9ms in a multiplexed setup.
Note however on the datasheet the Luminous Intensity/Segment is specified with IF = 10mA. I'd try them out first at a low current, then work up if the brightness wasn't sufficient. I might start with a 56K resistor for RSET with the MAX7219, but it could go as low as 12K. If you get to 12K and the display is still not bright enough, then external drivers would be needed, but I'd be really surprised if that was necessary. My experience is that most decent displays (like I'm sure these are) are plenty bright even significantly below the specified test current.