Just to avoid confusion for anyone still looking up this thread. Yes, it is possible to go higher than 256, the maximum is 1000 fps. The counter doesn't go higher than 256 fps, while it probably should.

For a lot of things, jj2 runs at 70 fps. For very few things it doesn't. In theory, running games with a framelimiter would reduce unnecessary computing power, but in jj2s case, the frame limiter itself is not working ideally on modern systems, and it struggles to select the right frames out of how many it's able to compute. So in a way, the game runs worse on lower /maxfps on better systems because the framelimiter is sort of being overloaded. This is why I set /maxfps 1000 for the smoothest experience, eventhough it will compute a lot of frames and puts a strain on my modern cpu.