Every year during the Christmas season, I run my two scale Legacy Polar Express engines on the same track for 4-7 hours at a time. I do not run them in a lash-up because I have found that if the consists they are pulling are not identical, and mine are not, one will slowly gain on the other, so I start at a certain speed step and adjust the engines until they are running as close to the same speed as I can manage. This may not be an issue if you are talking much shorter running sessions. The best way to see if the lashup option is good is to put both trains on the track with their full consists and put one engine a track length or so behind the end of the other train, start them up and get up to the speed you want and observe the gap to see if it is noticeably growing or shrinking after 10 minutes of running. If the gap doesn't change, then the lashup is OK, and if it does change, then it it a matter of just setting one engine to the speed step you want and finding the sweet spot speed step for the second engine.
In either case, you still have to pay attention, because I have had, on occasion, one engine or the other stop for no discernible reason.
Andy
