I use the biggest EaO I can fit ..and before that, the biggest PureOne I could fit. I use sandwich heat exchangers so that limits me on the wife's 4.0 to a PH3614 size EaO57 ..but I can still fit the EaO42/43/96 ..and maybe the EaO15.
Edit: I don't know if this is all 4.0 in Wranglers beyond a certain year, but my neighbors 05 Rubicon has a different setup than my 99/02 TJ's. The frame is WAY down from the filter and the control arm/motor mounts are way removed from the filter area. He could put a 51776 on his if he wanted to.