I have a 5 string bass and I love to tune down as much/far as possible (obviously while still being playable).

I managed to get my bass tuned to ACGCF and more recently G#EADG (if the rest of the bass was lower the G# would be too floppy), but that's as far down as I can go and still have it playable.

I can tune my 4 string bass to AEAD, and only the lowest string is a little too loose.

I tune one of my 6 string guitars to Drop B but can achieve Bb or even B standard. (I have much heavier strings on it though). I tune my 7 string to either standard, Drop A or occasionally for kicks Drop G. I REALLY want an 8 string so I can tune it to an octave below standard, or Drop E (I know, I'm insane). I just like testing the limits of tuning.

I'd actually also like a 6 string bass, and I'd tune it to probably FBEADG.