>
> Howdy,
>
> Use {\addfontfeature{LetterSpace=5.0}STUAGNL} which should isolate
> the LetterSpace change to that group and save you a second
> \addfontfeature.
That did the trick: I'm nearly back to my initial time. Thanks a lot!
I had no idea, that it actually made a difference how I would switch
a feature on and off...