Purely from reading many hundreds of posts and asking endless questions. As I said, I have never used a CNC machine before but have cut a fair bit by hand and that seems to back up my theory on speeds.

dont forget that I am only concerned with lower power cutting, as I'm in a home-shop and very limited on power etc. A 50A cutter is about the limit, I know that would cut ridiculously fast on say 1mm sheet but it's variable and more control can be had by lowering it to 20A and running at a more controlled pace.