I smell BS in that "6000 is the limit for dyno runs" rule. Sounds like an old rule of thumb from the days before electronic rev limiters existed. There's all kinds of engines out there that rev much higher than 6000 rpm. I think my wife's car revs to 8000 or 9000 rpm. You wouldn't stop the dyno at 6000 on that engine. Modern engines are designed to run safely (and often even continuously) anywhere within the rpm range all the way up to the rev limit.

Clickable images for full size seems to work nicely now. It' just missing the message that explains that it can be clicked for full size.