I've not come across that problem before.
Could you upload a CamBam drawing (.cb file) and I will look to see if I can spot anything?
If Mach is reporting the correct speed but not moving at that speed then is sounds like it might be a Mach3 configuration problem. The only other thought is that your drawing units may be set to millimetres rather than inches (set from the units drop down on the toolbar). The the gcode would be read as 10mm/min rather than 10in/min .... but the size would be wrong too.