As much as I hate Chicago traffic, I think you would be okay with I-80. There is a lot of construction in the St. Louis area. I just came back from Ft. Collins via I-80 with no major construction issues and relatively light traffic until I turned off on I-88 to go up to the Northern suburbs. Just be careful as you go through the Chicago area (from Joliet over to Portage, IN), there are some really scary drivers out there and road rage is not uncommon. Have a good trip.