"I really would like to see an objective 2D quality benchmark as I don't think there is such a thing."
There won't be. The problem isn't chip level at all(at least, not with current boards). Want to see better then Matrox G400 2D quality? Hook a Hercules DDR GeForce up to an SGI 18" LCD display via LCD.
The problems with 2D image quality are all about signal integrity from the board to the monitor and then how the particular monitor deals with each different signal. For instance, the same Herc board I mentioned above that has stellar 2D quality using DVI out will most likely look quite sub par hooked up to a Sony G400 21" monitor running 1600x1200@85Hz. Instead of the signal moving directly from the chip to the screen, it needs to be converted from digital to analog via the RAMDAC and then passes through RFI filters and then is received by the monitor itself which needs to process the analog data. To benchmark something like this, you would need an external piece of hardware connected to the vid card instead of a monitor and then have it callibrated for the exact settings of each monitor to determine a good signal for image quality.