Like all things perceptual, an exact answer is maddeningly difficult to pin down (individual to individual variation, subjective issues like ambient light, etc)

Like all things perceptual, an exact answer is maddeningly difficult to pin down (individual to individual variation, subjective issues like ambient light, etc). Even at 10-bit you could in theory see banding if your color discrimination were good enough, I think. It depends on the material... but the 10-bit displays I've seen look awfully, awfully good. (And the ability to represent more dynamic range starts to matter -- you have to have a wide scale to show off the bit depth, too. A monitor I saw at NAB this year has two backlights and can show off a lot more light... campfires glowed, headlights looked like they were bright, very real... that's the real direction for displays, I think.)