I'm hoping someone can give me a fix here. I've got a new system, and a new TV for use as a monitor. The card is an ATI HD 5770, TV is a Vizio 42" with 4xHDMI and 1 x RGB (vga). TV has no DVI

So here's the problem:
1. If I connect with HDMI cable, the screen is like "ultra sharp". not sure how to describe it better. Every blackish pixel pretty much has a white halo. I tried changing all the settings on the TV, tried doing color calibration in windows, nothing will get rid of it. Called Vizio support as well. I tried all 4 ports, and tried a second HDMI cable from a different manufacturer.
2. If I connect with a 6' rGB cable (ATI card has dvi out, and they supplied a DVI-to-RGB converter), the screen is perfect: beautiful. What I would have expected from the HDMI.
3. If I connect with a 12' "SVGA" cable, the halo thing isn't there, but the screen won't adjust to 1920x1080. it shows a few options, but basically only 1024x768 works, the rest go to a black screen. I think the highest option was like 1440xsomething.
This is a head-scratcher to me. The 12' SVGA cable I got online looks like it has about 3x the shielding of the cheapo 6' VGA cable, but the 6' one produces full 1920x1080 resolution.
My problem is that the PC is located about 8 feet away from the screen, 10 if I don't want a cable hanging straight in the air.
Anybody ever run into anything like this?