Normally I'd say bigger is always better, however if you are getting a FF without Side Image (Sonar / DI only) the the height of the display may be more important than the width. The 4x is only .7" smaller than the 5x. This is measured diagonal across the screen.
Like said above GPS is not just to keep you from getting lost.
I've never been good, But I've been Lucky!
I don't Lie or Exaggerate, but sometimes I remember BIG!