So maybe I cut/pounded more than other people in the front wheel wells, but I did actually run 285/75R16's on 16x8's for a short while with only about 1.5" of lift in front. I didn't have a problem with rubbing. So even if the rear is shorter than expected, I still think you could deal with it OK in the front.

Back to the topic of 906's in the rear, I think they sound like a great idea since some people get more lift then they want in the rear even when using the 890's. (I've heard 2.75" with 890's when there's no other mods). Go for it with the 906's and be sure to report back.