Thank you for the answers. One of the grades of my layout under construction is 3% and i was concerned.
My Athearn GP-9 will pull about 10+ freight cars up my 2.4% curved grade. That's 2-1/2 cars per powered axle. So I use that to approximate maximum train length for consisted locos. That approximation (it will vary by loco, e.g., a BLI 6-axle SD-40) would mean I would expect the GP-9 and SD-40 together could handle 10 plus 15 or 25 cars (a long train for my smallish layout). I do run the GP-9 with two Kato RS-2s and that means 12 powered axles, 30 cars.
Paul
Modeling HO with a transition era UP bent
On my clubs layout we have a branch line with a very steep grade. Single locos pulling maybe four cars up to the top. MU'ing two locos enables them to get twelve cars to the top. When MU'ing locos, speed matching should be done to have the locos running at the same speeds. A loco running too slow or too fast in the consist will hinder the ability of them to pull the train. DCC also lets you use distributed power. A pair of loco's at the front with another loco in the middle or on the rear pushing is prototypical, but depends on proper speed matching.
I'm still learning DCC. Now here comes my dumb question...when doing a multi unit operation in DCC, is it like real locomotive action, meaning, can the multi unit locomotives pull more rolling stock up steeper grades?