I only have a 5-string... so can't answer the question EXACTLY as asked. But, I've recently (literally 2 days ago) decided to see how low I could tune it. I have it down to F#, with relative stability... though it's really, really low tension. Thankfully, I am running XL Chromes, which have a 'tense' feel to them as it is, in spite of the literal tension.
What I'm debating now-- before I play on the weekend-- is if I'm going to feel comfortable with the adjustment to keep it this way? Honestly, I probably won't play much lower than I do now, it's more a matter of moving further up the neck while still maintaining the same "tuning" I had before. I'd still be BEADG, except that would all start on the fifth-fret. I almost never use anything on the G-string, which is why I've considered this. I've been enjoying moving up the neck, but if I'm going to play "bass", I haven't enjoyed the increasing frequency, as I move up the neck, if that makes any sense.