We just got back from our big trip out west, and figured I would update this thread with our experience taking I-80 south of Chicago.
In my opinion, the choice to take this route was probably the right one. Fuel is a bit more expensive across 80 between PA and Chicago, and the tolls are ridiculous (I think around $40 for our rig) but it was definitely a clean straight shot to get to where we were going. I-80 just south of Chicago had very little traffic at 11:30 on a thursday night, and all went well. We ended up at the walmart of our choice in Ottowa.