OK, my favourite tuning on my sevens has consistently been Ab Db Ab Db Gb Bb Eb for a while now. Really versatile for basically everything, BUT...
1) I miss having the extra high notes from when I tried tuning to D and adding a high G string.
2) Having the sixth string dropped makes it harder to travel across the board in octaves, which I really like to do.
On an eight-string, I'm thinking of this arrangement...
Ab Db Ab Db Gb B Eb Ab
This would obviously require an octave4plus string on top, but it would mean I could keep that bass string arrangement (with the option of dropping the bottom string another tone to F#), whilst still having the same pattern as a standard tuned six for the top strings, and the extra high notes from the D-G tuning.
What does everyone think?
Do it! You know you want to.
That tuning seems like it would work very well. Go for it.