Why I upgraded from crop body to FF?
The perceived improvement with low-light shooting when accompanied with awesome glass.
How was FF?
Don't know. Hard to say when one hates the system.
Why I am going back to a humble D80 and DX all-in-one?
Meh. Crop has worked well for me in the past. Don't need the fancy 5D2.
Research properly as I didn't.
Thanks for all the replies and suggestions! Have certainly cleared some of my doubts regarding crop vs FF...