Wanted to provide an update to my tweaked LG PA6500.
I already had them tweaked before but didn't really want to push it
Decided to unmount it and cut a hole around where the voltage pots were for easy access and adjustability. Not sure if the number of hours on the panel changed its tolerance somehow, but I was able to adjust STEP_UP all the way clockwise now without pixel misfires and the blacks deepened by quite a bit. Next, I turned STEP_DOWN all clock-wise and predictably, the screen went berserk, but the blacks deepened even further. I backed down barely from this until the misfires were only barely apparent on close inspection (not all the way to the way I had it before).
The result is WOW!! I didn't think LG panels could get this black. I put it side-by-side next to my Panasonic S60, no slouch in black levels itself, and I would've never believed it, but it makes the S60's blacks look gray in comparison. The inkiness and depth is outstanding.
A couple of side-effects. It takes like a minute and a half on a cold startup to get to the panel's full contrast. Also on a screen with no signal such as the LG logo with a black screen with no inputs, the noise, pixel mis-fires run rampant across the screen, but if content actually calls for an all-black screen like on a blu-ray, those misfires are gone. Strange.
Regardless, I feel this is a small price to pay for the blacks I'm getting. Very happy that I breathed new life into my plasma until I buy an OLED.