I did some further testing yesterday evening. It turned out, that so far the Hurricane Rotol is the worst considering the gauge issue.
(If you set it up in FMB with a speed of 250kmh, it actualy flyes only 206kmh (128mph) by the way...)
Flying
206kmh the Hurry should travel a distance of
10,3 km in 3 minutes. the actual distance flown is
13.3 km instead. That's a
33% too slow speed gauge!
I'm wondering if the stall speeds and such crucial values follow the actual speed or only the speed gauge. So landing speed for example could always be too high because the wrong speed indicator