I've been searching on the web for an hour or so and I couldn't find much information about PROGMEM access speed.
I'm currently writing the code for a POV globe (I have not yet received the components, but they are on their way!) and I realised that I'm running out of SRAM (only 2.5 Kb available).
I would like to use Flash memory to store my data, but my question is: will it be fast enough?
I would have to do at least 92 160 accesses per second, and 245 760 at the most.
If it is not fast enough, I can do two thirds of these accesses in SRAM and only the third in PROGMEM, but again, same question here...
I dont have a hard number for you, but it does take extra steps to get data from PROGMEM so it will be a little slower than normal SRAM, but at that point your counting cpu cycles at 16Mhz (what is that like 64ns per cycle) ... using arduino your wasting 10x the cycles switching a pin over banging the registers, so it may not be enough to effect your project
I am saying the best way to find out is to check it yourself, but I think it would be fine, as your speed problems (if you have any) is more likely to be getting the signals out to the LED's due to switching speed in the arduino libraries (thats the cost of being portable and easy to use across many chips)