It's interesting to note that I recently had a Sammy 50B860 set right below the 500M in the living room, and I fed a 0 IRE simultaneously to both late at night when it was dark in the room. You know how the Pio starts out gray at first, and then gradually takes a couple lower steps until it reaches its true MLL? Then after 30 seconds or so it totally blacks out and the panel shuts down, going totally black into standby. Well after a short bit the Pio shut off, but the Samsung was still lit up like a Christmas tree on the 0 IRE signal. I grabbed the remote for the Pio and hit some button to "wake up" the Pio out of its hibernation. Of course when you wake it up it once again cycles through the three levels of deepening blacks until it settles at its lowest level.
When I hit the Pioneer remote to wake it up and get the 0 IRE signal showing again, it looked pretty much exactly like the Samsung below it!
So the Sammy B860 on a 0 IRE glowed at the same level as the 500M on its brightest setting, before it settles to its true level.
If I raised the brightness up 6 or 7 clicks above normal on the Pioneer that was approx. where the Samsung was in black levels.
The Pio had nothing on the Sammy for colors, sharpness, processing however. The Sammy does exhibit line-bleed much more than on the Pioneer, which is so faint that it's about as good as non-existent. The Pioneer is clearly superior at resisting IR as well. The Pio has better aspect ratio controls for zooming/stretching/cropping the picture as well. Other than that they looked remarkably similar on content that did not have large portions of black on the screen.