I play with dollar tree foam boards for making foamie planes. Just for pure fun.
I am by no means a pro at this but with my 130 watt I have a couple of settings for different uses.
I know you trying to concentrate on speed where I am concentrating on partial cuttings and scoring the boards.

speed 40 power 15 will cut straight through
speed 70 power 14 will cut through top layer and foam and not the bottom layer.
speed 70 power 10 will cut top paper only

I haven't spent a lot of time perfecting these settings but they work pretty consistently.
I think as my tube ages though I will probably lose my 10% power setting where the tube will fail to fire that low.
Only time will tell.

I haven't tried any speed runs on my machine. 70 Is as fast as I have been with it.
I don't know how fast it actually could get up to. I believe it depends on the intricacy of the cuts.
I would definitely talk to Nolan or Tom at Thunder Laser and ask what kind of speeds you can get.
I know with 130 watts of laser ( actually 80 -90% of that) it will cut the foam like butter so you will have plenty of power
for most any speed that you can get out of it.
Like I said mine is just for hobby use so I never have tried to push it mechanically.

Hope this helps some,

Gozzie