I just recently completed a new 5 deck 027 layout with a Marx 999 train set operating on each deck. Four of the decks receive power from a 275 watt Lionel ZW transformer, and one deck receives power from an American Flyer 100 watt transformer.
It is challenging to operate, because I have noticed certain performance inconsistencies among my fleet of 999s. In the linked video, you can see some of the locomotives are operating smoothly at lower speeds while others are operating much faster. In order to make this video, I trimmed the applied voltage to a level that was just north of stall speed for each one of the locos. This was also a challenge because I noticed that as runtime increased so did temperatures, and speeds. It seemed that everything sped up as the motors and transformers started heating up. Finding a stable operating point for all five trains was like trying to hit a moving target.
I haven't actually measured and quantified any of this, but these are just my initial observations.
I am interested in your thoughts and opinions on this.