Dvi = hdmi = display port in regards to image quality. Just a different connector.
not according to Wacom. on their website they state that in order for the Cintiq 24HD to support 10 bit color it must be connected via displayport. display port has a higher bandwidth than DVI,
I have GTX680 connected to HP ZR30w via DisplayPort. When viewing the ramp.psd (http://www.amd.com/us/Documents/ramp.psd) there is visible banding.
Here is how Photoshop is configured for 10-bit rendering:
http://www.amd.com/us/Documents/48108-B_ATI_FirePro_Adobe_10-Bit_FAQ_R5_Final.pdf
does the HP ZR30w support 10 bit color?
are you looking at the image in OSX or windows? I'm thinking that OS X may not support 10 bit color. Kind of a bummer...