With a 1.6 and a GRS 1 I think you would do just fine. I run a 30.8" tire now. I have a 1.6 8V that is carbed and it doesn't have any problems gettin up to 85 on the flats and 55 on the hills. As long as your not just a rock crawler I think you will do ok. With the GRS1 you get a 12% reduction in high range.
Some one tell me if my math is correct the difference between a 30 and a 33 is 3" 10% of 30 is 3. So if he went with a 33 and a GRS1 it wouold actually be 2% lower geared in high range then he is currently. Of course that doesn't take into account weight diff. and tire drag due to being wider either. I dunno I think it would work maybe?
Hey if you are willing to run 4.16 gears that would just help you more with the 5.12's and I dont believe you would lose that much top end power but then again it all depends ont eh weight of the tires you plan on running but I would just go with the 5.12's and 4.16 gears!
P.S. how hard of an install is it to put a tracker rear axle in a sammy hey if he dont want that I will take it but I really need a tranny and t/case as I have plans to run a dual case set-up I will pm ya