@Cuzzie Please could you post the link to that thread? I've got some mucking about ahead and would like to try some different options. I've got a Dean Rhapsody 12, I picked it up for <£400 about two years ago. Quality is way beyond expectation and it just doesn't go out of tune, it's very stable. It's the only bass I have that I haven't fettled in some way, the fret job is great.
From my experiences of an 8-string it was trying one that was the deciding factor in me getting a 12. Jeff also uses an 8 a lot (I've seen him play one live on RVM, Go and I think State over the years). Based on my Dean I think that with the width of a 12-string board and the area that the strings cover I could around an 8-string quicker so for trickier lines where more dexterity is needed it would be more like a 4. I have to say that when I swap from the 12 to a standard 4 mid-gig it's like putting down a rocket launcher and picking up a rifle.