I don't know Mariss and I have not used the stepper board from CamSoft. I have used the Galil boards with CNC Lite on Bridgeport knee mills.
I have got better than expected feedrates and rapids from this package.
There is a setting in CNC Lite that caps the maximum rapidspeed. It is called RAPIDSPEED for each axis. The system won't go any faster than this speed. CamSoft must be aware of this because it is the first thing I thought of.
Other than that all that stands out is the 5 to 1pitch and 2 to 1 belt ratio. I think Anaheim Automation only sells stepper motors so it may be the motor is stalling at higher travel speeds with this gear factor. Stepper motors will commonly stall at higher RPMs.
Power especially voltage affects speed. Check if your getting 75 V out of the gecko drive.