Bob,
Does your machine have a braking resistor? If not, consider adding one - it will GREATLY reduce the require dwell time, as you'll be able to make the spindle stop VERY quickly. That will, in turn, allow you to run higher RPM when tapping. With an ideally setup T/C head and g-code, the T/C head should be just about as fast as the reversing tapping head.
Regards,
Ray L.