I don't believe that machine is cutting at 300ipm (;-) I have watched a lot of machines run over the years and that is not 300 ipm.
At 300 ipm the machine moves at 5"per SEC
If you look at the first cuts at 100 it takes a five count to cross the block , the 250 it takes a five count, at 300 it takes a five count.
Just because Mach shows 300 does not mean the machine is moving at that rate. I can make th LPT version show the exact same thing.
(;-) TP