Rubare - that is the magic question! I am wondering the same. 1st off you certainly don't want to stagger/different widths from front to rear, etc. that isn't only not recommended it's a big no-no! Some people don't realize, that even if you have different tires on front and rears with AWD that can even screw up your drivetrain after time.
I wanted 22" but worry about them fitting, now willing to take the chance, 21" rims seem to be slim pickings so I will probably stick with 20" x 8.5 like the factory wheels