I was cutting some ply last night. 4mm single-flute carbide cutter, 24K RPM, 2000mm/min cutting speed, 3mm DOC. Probably could have gone at it harder but like a lot of my jobs, I was cutting fiddly bits and I wasn't confident about the hold-down method stopping the work moving. After all, with a handheld router I would be running these cutters at 26K RPM so that's not a problem. After that, it comes down to rigidity of the machine and how well you can clamp things. Just keep winding things up until it breaks!