Their advice is also that higher RPM is better for an engine than lower RPM (at equivalent power), because higher RPM results in lower cylinder pressures. This contradicts the common sense view, that making the engine turn slower means less wear.
That's not quite what Deakin says.
From this we can see that there must be a balance between slower/leaner, and faster/richer. For high power, maximum-performance operation, you should run richer mixtures and higher RPMs. For low power, maximum-efficiency operation, you should run leaner mixtures and lower RPMs.
As a rule of thumb, that's very sensible. And sure, we're talking about climb here, so we're likely to be at high power.
The key issue is what is tolerable for the engine in terms of cylinder pressure and cylinder temperature. I can't help thinking that temperature is a very much more important factor than pressure, just because of the way chemistry works. Small increases in temperature can make huge differences in physical and chemical processes.
It's very difficult without instrumentation to decide if a particular operating regime is bad for a particular engine. Even that 7% difference in ICP is difficult to assess -- sure, it could put the engine in a bad operating regime, or it might leave it in a perfectly safe one.
In the same way that everyone wants the lower specific fuel consumption associated with proper leaning provided it does no damage to the engine, I'd like to have the lower SFC associated with lower RPMs with the same proviso.