I consisted seven diesels on my HO layout, a mix of Atlas, Intermountain, Stewart/Kato, original Proto, and a remotored Front Range Geep -- six LM3s and one LM2, four with PBMs and the rest with TCS KAs, three with speakers -- and ran a 30-car train up my 2.5% helix and back. No problems, except at the end when I was drilling cuts in the yard, I got a short for no apparent reason, cleared it, then found an Over Maximum Voltage alert for the Atlas GP38, Proto BL2, and Intermountain F3. My track power was an NCE 5 amp base station, so maybe exceeded available power?
I quite enjoyed running a long train with max power on my double-deck 21x15 railroad. Changes the playing field for future op sessions.