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.)
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.)