If your using R&P then chances are you'll have a high pitch so lack of speed won't be an issue even with steppers.
Steppers are a lot easier to setup and get working and they are much cheaper. They are just as accurate as Servo's if tuned correctly with far less hassles.

The Only reason I would consider going to the expense and complexitys of servo's is if the Gantry was heavy or I need very high speeds. Speeds well above 7.5Mtr min are very easily achived with steppers and depending on Gantry weight they most likely won't need to be 12NM either.!

What do you plan to cut at above 7.5mtrs/min.?