I am not familiar with mach 2 but generally in can be summed up just like a computer. You can play games on a 486, but when you try to run too much information through them they slow down. SO when I post HS machine code, it is generally thousands of little lines, sometimes 1000 in one inch, so what you get is if the block processing time of a machine is say 75 per second. You can assume the following 1000(lines)/75 (lines per second)=13.33... (time to cut one inch). This would be regardless of the programmed feed rate.