If I want to export a high quality intermediate from Aspect HD using Premiere Pro 1.5.1 to bring into a third party batch video encoder as is my custom: What's the difference for me to choose to export a CFHD versus a Cineform HDV AVI file?

CFHD is the FourCC code that identify the compression. As for export options you want "CineForm HD Export". There are two other options in 1.5.1: the older license Adobe has (you don't want that) and using Video for Windows -- neither are as good as "CineForm HD Export".