I could imagine that all or most review sites get their review devices from the manfuctures directly. And most likely they were handpicked before. That's why most independent consumer review services buy their test subjects from the shops and sometiems get a different (more realistic) result.
As long as you don't wipe your phone through clockwork-recovery before flashing any ROM your previous data and settings will stay on the phone.
It will just be updated with what comes from the new ROM package.
However this mainly works between ROMs from the same developer, but seldom between ROMs from different builds or developers.
A clean install (full wipe) is always recommended to avoid issues, but not essential as in your case
gforums 2.2 ROM is till in a very early stage, but fore me it's already suitable for daily use.
For me it it is stable and very responsive, making the device fun to use.