I would be so bold as to assume that you won't be off-roading if you are going to a 20" rim with a shallow sidewall tire. I have a 2" lift (RC budget boost, 17"x 9" UltraWheel rim with a 4.75" BS (+12mm Offset), 265-70-17 (32") tires with very little rubbing (front or rear), have not done the PS or Rear Fender mod yet). I have stock struts in front but did add the MLLs (for F-150) in the rear which greatly improved flex (sway bars removed) and it now sits at 21.5" front and rear, nice and level. I have no clearance issues with the upper ball joint stud, actually looks like I have more clearance than stock and considering going to 285-70-17s(33") soon.
Black WK #139
05 WK, 5.7 Hemi, 2" R.C. lift, 32s, K&N, MagnaFlow, 4xGuard Skids, Custom Rock Rails