Has anybody noticed that the reading velocity using speech.start() differs between iDevices? Using the value 0.5 is fine for my iPad but it is much to fast for my iPhone. A value of 0.1 is much more appropriate there. How come? :-)
Perhaps that is relative to the device's default speech rate... have you checked what that is set to in the settings app? IIRC the slider for that is under General > Accessibility.
@dgelessus Your suspicion was right: the speeds seem to be completely different to begin with. I found a slider in the voice over section of the accessibilty setting. To get a normal speed on my iPhone I have to set the slider to about 0.1. Maybe this is a difference between 8.4.1 (iPhone) and 9.2.1 (iPad)? The value of 0.5 seems a lot more natural for a medium speed than 0.1 so it may have been changed during a release update...