Read the other thread, lots of good info there.
Moving the diff 1" forward results in the same clearance gain as lifting it 2-3" (this would be at the floor/firewall area that is prone to rubbing)
If your budget allows for it you might want to check into some Alcan's through ORD. They're set-up so you end up with ~6" of lift, 2" longer than stock front and rear (49" fronts, 54" rears). They'll ride better and flex better than anything short of a coil sprung buggy...
They are custom tailored to your truck, and the type of wheeling you plan to do. I bought a set from Blk87K5 a couple of months ago, and the center pins are located so that the front diff moves 1.5" forward and the rear 1.5" rearward. The rear springs are 2.5" lift springs to be used with a shackle flip and the fronts are a 6" lift. No saggy butt either. There is no comparison between these spring and anything 'off the shelf'.
There is also no comparison price wise, but you get what you pay for.
Of course this leads to the need for very long shocks, brakelines (you'll need longer ones anyways) and long slip joint driveshafts capable of a lot of angularity. You'll also need crossover steering and proper bump stops.
Rene