They're actually pretty similar.
The Xtreme package has ZQ8 suspension (1.5 inch drop springs, rear sway bar, stiffer front sway bar, performance shocks, 16x8 rims), Xtreme specific rims wrapped in 235/55/16 rubber, ground effects, quick ratio steering box, and a body color grille.
Toyota did do a good thing in not offering a 4cyl or auto trans. option like Chevy did.
But I suppose, I was wrong and there is more similarity then I thought. However I find the X-Runner to be significantly better than the xtreme's.