What is the RPM rating of the motors? Typically servos have RPM ratings of 4 to 5 times the steppers. They work better at higher RPM (VS steppers that lose torque with RPM). Normally your gearing needs to change and you can trade the excess RPM of the servo for added torque and resolution.
Do some math. Take the top RPM of your servo at say 70volts and see what that translates to in IPM using your current gearing. Anything over the target rapid speeds of your table is just wasted. You will often find tha you can use smaller servo motors than steppers and get the same speed and torque (and much better resolution).
Typically changing from stepper to servo is not a bolt-on upgrade unless you are willing to leave a lot of potential unused.
There are pro's and Con's for each type of drive. There is no clear defining reasons to do or not do either technology. Statements that steppers are "old" technology and somehow inferior are gross convolutions of truth. Conversely saying that servo's are too complex and wear out sooner have some amounts of truth but should not weigh heavily on the decison.
The bottom line is: How big a load do you need to move and how fast. Secondary consideration is resolution. Servos can still lose position (get noise in your encoder lines and you will see what I mean). The cost is becoming less of a point as well. Usually the cost is for more/bigger power required to run the motors.
We stand agnostic to either approach and try to guide our customer based on the target usage of the machine rather than old-wives-tales (or slick marketing spins).
Tom Caudle
www.CandCNC.com