The way I understand it, you need to consider 1) max feedrate, 2) starting acceleration, 3) max acceleration. Ryan was testing the impact of running the Rambo board at 12V vs. 24V recently, and gave us some numbers for limits. You can see his post here.
My takeaway from his numbers is that I will likely suffer some sort of laser output quality issue, or Rambo board might not handle g-code throughput, before I reach the speed limits of the machine.
Personally, I’ve just started playing with laser engraving and working with these settings. I set them through g-code that is included as a start script, and I don’t save them with an M500. That means when the control board is rebooted, it will revert to the slower settings, so when I put the router back on, I don’t have to think about making a change (or having an accident). My current settings are:
M203 X900 Y900 M204 P1200 T1200 M201 X1200 Y1200
And the max feedrate I’ve used for an engraving so far is 125mm/s.