I am not sure what parameter you are using to set the speed at 310mm / second. There are 2 basic things to check:

1) OPTIONS / PARAMETERS / OPT.MOTION
2) MOVESPEED / TOUCHSPEED

The movespeed & touchspeed commands will be at the top of every program. These are percentage values and will never be more than 100. Touch speed should never be more than 5, you sure don't want to register hits at full speed! I normally use 80 for a movespeed instead of 100 to help eliminate false triggers of the probe. Other than this percentage, I do not know of anyway to change the speed of the machine, using the program. If you have a Sharpe32 controller, also check to make sure that the 'speed' setting on the joystick is turned all the way up, this also effects the DCC move speed of the machine.

The OPT.MOTION parameter will allow you to change the acceleration for each axis, which I do not believe is the speed it will move, but how fast it gets to maximum speed (I may be wrong), so I don't think this will help the over-all speed of the machine, but a higher value will get the machine to top speed quicker. If the number is too high, it may cause lag errors from the machine not being able to accelerate as fast as the drives are trying to make it accelerate.

I hope this helps.