Can't help you on 67, but if you continue on a little further to the west side of Memphis, I-55 north and then I-57 to Effingham IL is a little used interstate that's real easy to rack up miles quickly on. Plus you get to skip St. Louis!
When I picked my LT up in Memphis, that's the route I took back to Indy. Not as picturesque as other routes, but good for quick miles.