To add to that, in my experience too, the plastic backed motor cans have vastly more grunt than the metal backed versions. Just two (plastic vers.) drive the heavy (2.5kg) lifter and spinner KE pay-to-drive bots really really nicely. The lifters are especially impressive as the wheels are at the back and they have a scraping wedge.

I bought some 500rpm motors for them thinking the 1000s (ebay) would struggle. After fitting them two things were evident; they had less torque despite having double the mechanical advantage and they were very noticeably timed in one direction. So much so that trims couldn't sort it in conjunction with BB10a ESCs.

I have metal endbell 1000s in Newton and they are also markedly underpowered. Much less nippy drive than the pay-to-drives despite weighing over 1kg less.