Ted, just to clear up a point. The Rotax is a fine motor, as is the X30. I’d suspect the Rotax could go nearly twice as long between rebuilds, but as Rob stated is quite a bit more expensive.
You did mention road racing, in which case if you live on the East coast and run with the WKA / WKC the “Leopard” is far more popular!!! We typically run 5 to 6 road race events per season, all being at least two day events with approx. 1.5 to 2 hours of run time per event. We have the Leopards totally rebuilt every TWO seasons. That will give you an idea of maintenance levels. My Uneducated guess for the Rotax would be 3 to 4 seasons.
Also as Rob stated you can adjust on the fly with the Leopard or X30 and don’t need a weather station to calculate jetting as the Rotax requires.