Hello,
10-bit doen't work on OSX by now due to lack of drivers settings.
It DOES work on PC. This is the link for reference and testing info, including the 10-bit test file :
http://www.imagescience.com.au/kb/questions/152/10+Bit+Output+Support
Here is my setup:
Nec PA271W (10-bit monitor) DP connected
Ati FirePro V3800 (10-bit card) DP connected
Adobe PS CS5 (with open gl setting to "advanced")
Inside my Mac there are NO "real" drivers for the V3800, so though it works fine it is impossible to activate 10-bit support through the driver. It is generic, allows for QE/CI acceleration but nothing more. The ramp test file shows banding.
On my Win 7 machine, same config, but we got the catalyst suite. So activate 10-bit in catalyst window, reboot, the ramp test file shows NO banding, everything is smooth.
The problem in OSX is that you cannot activate 10-bit support in the drivers (there is no such thing as a catalyst settings window as in the PC world), so it doesn't work.
Maybe by digging inside the kext that are loaded for ati, but not easy