What is the relationship between the saddle(?) and the bridge? Seeing as they're both adjustable, one would guess they'd have an effect on one another, though I can't quite figure out what it could be. Obviously strings would be tighter the lower the saddle.
Having read your post again, I must say that having the bridge high provides me with high action at the higher frets and low action near the headstock, though I haven't noticed any improvements (bridge used to be about halfway lower prior to this, leaving low action throughout the fretboard. In both cases buzzing worsens closer to the body).
Body/neck joint on my SG appears to be at the 19th, which when fretted along with the 1st fret leaves a VERY little gap. So much so, that I'm not sure if the e-strings windings are touching the 7th fret (or any other) or not. This is too close, yes? If so, do the symptoms apply to the diagnose (truss rod too tight?)?
Also, I don't remember noticing this buzzing issue - only being unhappy with the overall sound - while I'd switched from 9's to 10's and from 10's to 12's without touching the truss rod at all (hey, I just play the damn thing!), though then again it would have been harder to notice with the poor amp and pickup I was using at the time...