C128 Graphics Booster.............I am stunned !!!!!!!!!!!

[AmiDog]

AFAIK the graphics booster just adds a few new basic commands and came with a 64kb VDC RAM upgrade as most C128s only had 16kb which is not enough for the higher resolutions. (64kb VDC upgrades can usually be found on eBay.) The C128 VDC chip is rather flexible and support interlace, so it can easily handle 640x400 and above, assuming your monitor is up to the task. (You need a monitor which can handle RGBI.)

[AmiDog]

Look at the resolutions it provides. The VDC only gives 640x400 in interlace mode.

No it doesn't. The VDC can be setup to provide just about any resolution as you can freely set just about every timing aspect of it. Any VDC with 64kb RAM can do 720x700. Think of 640x400 as the pixel resolution and 720x700 as overscan if you like.

[AmiDog]

Wouldn't anything beyond 480 vertical be outside the viewable range of NTSC?

Good question, I'm in PAL land so I don't know for sure. But maybe a CGA (or compatible) monitor required to view the RGBI signal generated by the VDC does not have PAL/NTSC issues, or the highest resolutions only work on PAL.