The Fuji materials use sigma-grain technology, their version of t-grain. It results in a much sharper B&W image with much better enlarging capability via scanning. I also agree that the Fuji prints in B&W and color are more resilient to the environment (scratches, pinholes, drying faster, etc). I mourn the loss of 4x5 sheet film. I will mourn the loss of integral material for my SX-70. But, when I opened the fridge to review my stash, I noticed that most of the boxes are green, rather than blue. Fuji instant material is great stuff! I order from B&H.
I easily enlarge my 3.25 x 4.25 pack films 3-5x with incredible results. I've posted a hybrid technique on the Flickr Polaroid group.