[Kevan]

I don't bother 'breaking in' motors

...and if you throw parts together you're not winning ANY races

I'd say 'swollen' (aka overwidth) tyres are worth more on track than a few hundred rpm.

Incidentally, motors can improve or degrade.  I sent a Corvette Grand Sport to the last real IPS Proxy (just as Covid started), it was a 14k motor limit event with categories for rear motored, slim motored...and front motored cars which the Corvette was.
The H&R Jack Rabbit in the Corvette went tachoing at 14k and came back tachoing at 16k.

I've also seen brand new motors fail on their first night (maybe it IS a good idea to break motors in to find these duff ones before taking them to a race meeting)