I had a 3200 and after that a 4990, and mostly scanned 35mm with them.
Took me some time to realize that one side of the 4990 was poorly focusing.
after some experimentation, I realized that the glass was probably slightly tilted.
I tried the same with my father's 4870, and the same problem arised, although not as bad.
I'm not sure (was a few years ago), but I think I checked a V700, and it was ok, maybe after playing with the holder height.
My conclusion at the time was that the sample variation is much more a problem than the incremental improvements between models.
I'm not sure if this is really relevant at 4x5, but I don't see a reason why it wouldn't be.
Today I would buy either a 4990 or a V700, but only from a source that I can easily send it back for a replacement. I would thoroughly check focus on five spots on the glass (four corners and center) and decide to keep it or ask for a replacement.