That is a very fair point and i agree with you on that one....
I am in the position i am as the tuner that sold me a part did not do his sums correctly and a a result i have blown the HG twice.
the limiter on an OE car is or should be set to 4200 - that is the engine max load rating; mine however came out the factory with a much higher limiter than that - before i fiddle with it.
However with all that said i have toned the fuelling down from above 4200 rpm as i just dont need to use those revs.
It would be rare that a derv would deliver more torque at 3000 than it did at 4000, just due to the way we usually have little turbo's - but again i agree with the sentiments disels are just not designed for reving - unless you drop the compression ratio to counter the increased cylinder pressures that the lower time for the various cycles then require.
but as soon as you do that you loose the efficiency and make cold starting harder etc..
hoo hum.. tuning something on a low budget compared to what the motor manufacturers spent millions on is never going to be an exact science, nor an easy process
