Truth is I am not s specialist concerning foam. I cut only once before a couple of weeks when I was demonstrating some 3 d job setting to my friend on the yellow machine I made for him.
So without knowing anything I started at 4500mm/min with 3 flute straight 6mm carbide bit. The cut was perfect. Spindle was 16000rpm. I pushed it somewhere to 8000 mm/min where was still acceptable the finish.
Now I have to tell you that the machine is extremely sturdy. I suppose that with the proper bits for foam , some air stream at the bit, 10000 mm/min will be no problem at all . And this cheap construction foam.
what I want to say that the bits you use must be good, SHARP, and the not sturdy frame and z can and will play you tricks there, so take it slow and concentrate on making back some cash.

But it would be interesting to hear what speeds and feeds others and you are cutting foam at?
I'm very interested in this discussion cause one of the things I would do on the big machine I am making right now will be molds from foam. Not to speak of the paddle board I have a plan to make and some other stuff. Plus foam is nice for casting aluminum, molds or directly