Danny
Not an engine fitter or mechanic, except when attached to the pointed end of my own car, but 3,000 rpm was what I was told by a sadly now departed ex-R.A.F. engine fitter some years ago, he thought possibly slightly more in emergencies.
It would seem the Reno racers have left the standard Merlin far behind. A quick Google suggests 3,600 rpm and more, astronomical boost pressures and power outputs approaching 4,000 hp.