The repetier slider is a percentage of whatever is specified. So if your cut is 10mm/s and you set the slider to 150% you should be moving 15mm/s.
The test script is running each axis at its maximum speed, it should not work above that that explains the slider problem you had. maximums for my hardware as sold and beta firmware is 197mm/s X & Y, 8.7mm/s Z those are max. you can double that by going to 16th stepping but that’s fast enough for me.
The Z axis useful speed depends on what tool you have on it , and what material you are cutting. Once you find your values everything should work fine. The beta firmware slowed down the accelerations to allow for max speeds and high plunge rates by I doubt you could plunge and lift at max speed with a router on the Z axis.
Reply To: Z axis Shuddering and inaccurate