RE: *** CLUB SUPER TIGRE ***
For the old S-29 engine, a "nice, low idle" was anything below 3,000 RPM. Anything lower than 3,000 RPM that gave you more than 30 seconds of idle with a "reasonable" throttle-up transition was considered "good". "Reasonable" meant that you could crack open the throttle and the engine would come up without dying, but might have a brief hesitation. Midrange was good as long as the engine didn't load up and die when you throttled up from there.
Basically, if the engine stayed running throughout a flight with a variety of throttle settings and throttle changes, it was "good".
Again, any sustained idle below 3,000 RPM is good. Anything lower is just "gravy".