Heavy duty shackles with moderate lift (1/2" or 1") aren't a bad idea imo, but I wouldn't go any bigger. Having a longer shackle can actually increase suspension articulation if you have longer lift springs, which is why Rubicon Express includes 1/2" lift shackles with their 4.5" CJ lift kit. Large shackle lifts are ugly, protrusive, and will mess up your pinion angle.