Big fan of yours
Are you using the K2 39x25 (G?)?
Did you get the Steppers from K2, whats the spec's on those steppers?
I have the K2 39X25 with the upgraded Z axis, servo motors and a Porter Cable Router.
I use Onsrude carbide bit's.
I'm achieving 200 IPM in Hard Maple at about 0.002 accuracy with a 1/2 carbite bit at 0.25 depth.
The most important parts to getting fast and accurate cuts with the K2 cnc is having the upgraded Z axis,servo motors and good carbide bits. I would give K2 a call and get the servos, I believe there 300.00 for all three.
Tune your motors
If you stick to what you have and your motors are tuned correctly, jog the machine to see what kind of travel speed your getting without butchering the motors or the frame, this will be the max that your machine can handle.
After this it'll be up to your router.
Your bit should be clearing out the material giving very little resistance to the travel of the machine.
I spend around $75 a bit and they don't last long till there dull.
I would love to talk guitars and design softwear if you have the time give me an email. email@example.com
I also have some screen designs that work good with the K2 machines and other stuff.