replacing steppers with servos

what is involved in replacing steppers with servos.?
I have got my steppers set up to run at a max speed of 750 RPM, would
I need to change the gearing to suit the servos higher speed? If so
what is the ideal speed for servos.
Is there any problems tuning the drivers with the servo motors? do
they go out of adjustment with use?
my steppers are 450 oz/in, what size servo would I need?
Colin