Here’s a link to a mod I did for the eccentric nuts to keep them adjustable yet still very tight.
You might also look at the X Controller. Apparently it allows you to drive the steppers with much higher current, so much faster and more accurately than with the standard Arduino+G-Shield setup.
On my machine I’ve been running at about 2000 - 2500mm/min which would equate to roughly 75-100ipm with standard bits in pine, birch and MDF. I have all the standard electronics, so you should be able to push the speed considerably on your machine as well.