Digital BW, The Print

As everyone noted, you can't lower the iMac screen enough in hardware.

and yes, there is also a significant brightness difference across the screen.

ColorEyes (or BasicColor) adjust all 3 primaries to lower the brightness but that affects the overall levels.

In the end, I got a Dell 2209WA to use as my proofing monitor.  it was only slightly more than just the ColorEyes software and it solved all the problems.