With a 6" lift and a fender trim, you should be able to clear at least 34's for hard wheeling and 35's otherwise. I have a total of 7" of lift on my Choptop and no fender trim and 33's look a lil small, IMHO.
But you run into gearing problems. I would say that 4.10s would be adequate for 33's, and 3.73s the bare minimum. For 35's I'd say that you should have 4.56 or 4.88.
That's part of why I haven't put 35's on my choptop yet, still gathering the things I need to regear and upgrade my axles. Kinda wishing I would have put a D-35 and 8.8 under it when I first put the suspension together...