Hi Olaf,
I was there in 1991 and timed one stretch at 56 km/hr (35 mph). The Baldwins could really fly, considering the drivers were 31.5 inches in diameter. The Henschels could move right along too but were much rougher riding. The line has plenty of curves so speeds were generally much slower.
There is a rock outcropping past Nahuel Pan where we could get a last shot before the railway headed off into roadless country. I shot video there of a horse racing the train, crossing over ahead of it and then turning to watch the train go past, obviously enjoying his victory.
I got a cab ride in one of the Baldwins and noticed that the maquinista (engineer) drove with full throttle, regulating speed with the reverser. He wouldn't shut the throttle if he had some wheel slip, just quickly moving the reverser to mid gear and then back again.
Michael Allen