TOG@Toil wrote:
... I mean, what was max revs for a Merlin?

Googles

Hm. About 3000rpm. Just off tickover for a 'Busa.

I THINK that was the prop shaft - like many other aero recips
it's limited by 0.9 c at the prop tips at the top end of the tach.
But the crank was driven by pistons breathing gas though a duplex
compressor system - driving a PRU.
Then again - in War mode its overhaul time was measured
in the hours you can count on one to two hands.
Low compression heads on the Merlin
were the choice for civil airliners post war.

Brian W