I haven't got that far yet but will next week on a big router running a ESS.

what I can say is its faster and smother than M3 I ran a air test for 4 hours where it started it stopped on all axis, the speed change on the spindle was instant no lag using the speed over ride.

the machine I tested on ran a G540 and a superpid for speed control.

I have now converted it over to a laser running M4 and Darwin with a arduino as the laser control it works like a dream no laser on it yet I had it connected to a scope to test the laser output it was very fast changing laser power.

I ran a half arise test last week on a not properly set up laptop (what I new would not work well) to test a aerier ridden test on M3 and M4, M3 was out by a mile (1.24 mm on Z axis) M4 was just out (.42 mm on Z axis) turned the wireless internet off and antivirus the error when to .24 on Z in M3 and .04 in M4.

so next week when I run it on a correctly set up laptop I think I will have it to .00 something the test I do is a 1000 line Z axis movements at different speeds its done at 1000 line so if i run it and its out by the same amount each time I know how far it will be out in more Z movements.

if it out by a round about number like +0.02 then -0.04 then 0.00 its all good