I thought this would enable me to continuously overdub at e.g. 1x record speed and let the playback run at e.g. 2x speed. However this doesn’t seem to be the case as after the second round of overdub the record and playback speed have the same pitch again.

I loved to use the Chase Bliss Blooper this way. It would basically give me a really nice pitch shifted delay, since the blooper had one record “head” and one playback “head”.