It is a sad fact that many live steam drivers tend to drive too fast, a cursory look at live steam running on You Tube Vids will show this to be generally so. I have also been guilty of this in the past but slow running as a bit of a gained skill with time and to be honest reflects the real thing. My chose Harz Selktalbahn has or had a 20kph max speed limit some years back and that is not much faster than a pushbike can go unless an olympian is riding it. My own 3 Roundhouse locomotives are fitted with SSP SloMo devices which considerably tame their tendency to want to run away. Keeping the pressure down to under blow off of 40psi helps as well. Just look at any of the Narrow Gauge prototype lines in UK and the speed is quite slow, replicating that on our lines can give greater satisfaction plus less likelihood of derailments to expensive precious live steam dragons.