GT430, driver 306.97, DVI->NEC 20WMGX2, HDMI->Sony KDL-46HX850. Both displays behave the same. Both XBMC and 7MC x64 behave the same, with XBMC configured to use hardware acceleration. No codec packs now or ever. I'm using AVS709HD.
1. Dynamic range = 16-235: Blacks are visible down to 2. Whites are visible up to 253. I can fix the blacks in one of two ways: (A) For my TV, I can set brightness to 30, which is way lower than my BD player, which likes 48 (default 50). (B) Or, I can leave TV brightness at 48 and set the Nvidia video brightness to 43 (default 50).
2. Dynamic range = 0-255: Blacks are visible down to 17. Blacker than black doesn't exist. Whites are visible up to 233. Whiter than white doesn't exist.
I like (1.B) for consistency with my other devices like my BD player and the WTW. To make out all the wrinkles in the Media Center guy's white shirt, I do need to set Nvidia contrast to 53 (default 50), which doesn't have much effect on the AVS709 patterns.
The monitor is set to DVI-PC mode, not DVI-HD, and I didn't do anything else for it in the Nvidia control panel beyond changing the Video settings as already described. The TV's info banner indicates "1080p HD", and the Nvidia control panel's "Content type reported to the display" is set to "Full-screen videos" for it, and "Digital color format" is RGB (the default). The GT430 is keeping the TV in the same mode at all times; it's never switching between PC and HDTV timings. It didn't seem to do it even when set to the default "Auto-select", a big improvement over the behavior with my old KDL-40W4100. I'm guessing the HX850 is in HDTV mode, because "1080p HD" is what my W4100 reported in HDTV mode, and I'm not seeing any of the washed out colors at the desktop I would see when my W4100 was in PC mode. I haven't verified this further, though.
I really don't understand exactly what dynamic range is doing; it seems sort of backwards. Also, I'm wondering if using the Nvidia control panel to control brightness and contrast is hurting anything.