Hi there!
Thanks to Oshyans kind explanation I finally understood how the Mola displacement works.
I made some testrenders of Hebes Chasma just for comparison of resolutions:
Mola 16pix/°:

Mola 32:

Mola 64:

Mola128:

Astonishingly, the 16k bumpmap I´ve been using for years now isn´t that bad, comes close to 64:

And thats the goal:

stay tuned, although it may take me some time

Cheers,
Jan