Dog box, modern multiple units, 5 pole motors, They have no problem with long rakes of coaches.... Hornby Pendolino, 9 car units either being pushed or pulled race round.... traction tyres seem to make a big difference to a light weight power unit. I was initially a bit sceptical about the performance, but once tried out on track was perfectly happy...Hornby High Detail Hst’s, 8 coach pulse trailer car again no issue.... though I haven’t tried them on very tight curves and steep inclines.....
So I wouldn’t overly worry about the motor performance on generally flat track or gentle radius curves... i’m Sure that whatever the final arrangement is, it’ll be fit for purpose....