When I input the above transformer data and then ARSG info for the 9000 RPM motor (50 Hz), you are certainly at 1200 bps.
Bart, The actual true break-rate of an ARSG system will always be somewhat lower than the calculated break rate because gap presentations that occur near the zero crossing of the 60 or 50Hz AC will be skipped (the voltage will be too low to fire across the gap). The break rate will still be quite high of course.John