Hi Guys,
I would definitely run identical locos together. I usually run two little LGB diesel switchers or two Stainz locos together (both #2).
I have tried to run LGB and Playmobil locos mixed and with bad results. The varying speeds of the motors cause derailments and sporadic running...I never considered the wear on the gears/motor bearings, but it does make sense now that you mention it Richard.
One thing that's always bothered me about Playmobil locos is the lack of a coupler hook. It prevents a lash up. I haven't modified any of them with an added hook. I guess it wouldn't be that hard. Have either of you tried it?