Oh damn I could always run MS Train Simulator, but it would always crash after maybe 15 mins. I always got bored after that anyway, and Id just start up and see how many ways I could derail. Must have been a Rage 128 in there.
One of the routes was in the Swiss Alps and was all uphill/downhill for about 75 miles depending on which direction you started. I would put the Flying Scottsman at the top of the hill running light, spend about 20 minutes building up a massive and hot fire(as a train nut, I loved how much control the game gave over that kind of stuff) and then take off down the hill with the throttle wide open. I'd have to tweak the reverser a fair bit to keep the boiler pressure up close to the max, but with a big enough fire and going fast enough(meaning a lot of good draft through the fire) I could keep the cut off at around 12%, meaning lots of power going to the wheels. Doing all of this could get it up to 130 or 140mph by the time I got to the bottom of the hill(just as long as I remembered to close the firebox doors in tunnels).
Then I found out that there was a "config" file that set the maximum speed of every locomotive. I changed it to 500mph on the Flying Scotsman, and was able to get it to up around 300mph doing all the same as above.