Yeah, I remember someone trying to use a pair as drive and saying they were really weak motors, not good for drive...

12k rpm is not actually that far off what I had, if I remember rightly I was getting about 2000rpm on the wheel with those 51mm motors on a 4.5:1 reduction, with a 6:1 reduction on a set of S700s, I'll be looking at around the same on 3S which works nicely for me. It'll be better when I have the weight balance sorted by way of adding a disc mechanism and grippier wheels, but should just about do it.

Will certainly push the motors to their limits, but with enough air for them to cool down, they should be fine I reckon.