This is my experience with a Zenith Z50PJ240 (2010 model, presumably the same as the 50PJ350). I made the following changes, in this order:
Set_Up: Clockwise from 11 o'clock to 4 o'clock (max)
Set_Down: Clockwise from 1 o'clock to 7 o'clock (max)
Vy: Counterclockwise from 6 o'clock to 5 o'clock
So far, I haven't detected any problems caused by the changes to Set_Up or Set_Down. Vy gave me misfiring pixels if turned too far counterclockwise. Set_Up and Set_Down both had a significant, and roughly equal, impact on MLL. Vy seems to have a smaller impact, but turning it further counterclockwise does improve MLL even more.
With those three adjustments, my MLL has lowered from 0.026 fL to 0.012 fL. Also, image retention is now a much smaller problem. As a test, I displayed the info bar against a black background for 80 seconds. I could very faintly see some IR afterwards. If I had done this in the past (same contrast), I would have been able to very clearly see the IR; I would have been able to read the text in the box from my normal viewing distance, even if the bar had been displayed for only a few seconds.
I'm curious about Vzb after reading some of the comments here. I feel like colors are undersaturated on my TV in dark scenes with low contrast. Could Vzb have an impact on this... without affecting brighter scenes? I measured mine with a multimeter, and it is almost exactly 95, so I'm hesitant to play with it. I thought it was probably best to leave it alone.
Another question: while I've already got this TV open, does anyone know of anything (safe) that can be done to reduce buzzing? I think I remember hearing about people with Samsung plasmas removing the back cover and doing something to reduce buzzing, so I wondered if there was anything similar that could be done to these LGs.
Anyway, this was a major improvement. I was hoping that MLL might drop below 0.01 fL, but even at 0.012, it is much better than before. And the improvement to IR is a nice bonus.