I use to run 2 conventional locomotives (not MTH) together. The engines were the same brand and model and ran at about the same speed as John notes above. I found what was more important than the engine was the track. If you have your track wired conventionally and stop on a dead spot, when the engine gets power again, this could cause one of the engines to cycle out of forward and it would then have to be reset. Not a deal-breaker as its fairly easy to fix the dead spot.