200 miles per day -- that's my kind-a people.
As a Texan, you know what a great state park system Texas has, making for numerous routes to St. Louis. The quick way is I-35 to Dallas, then US 75/69 to Big Cabin and then I-44 to St. Louis. We left MO 1-2-07 and spent two weeks getting down to the valley (it's the journey, not the destination). We took 65 south thru Branson and on to Little Rock, then I-30 to Texarkana. Thence south on 59 to see the parks in the Piney Woods. There is a nice City Park at Burns Park in North Little Rock just off 65/I-44. There is nice park, county I think, on the river in Branson next to "The Landing" whcih is Bass Pro's latest addition with a lot of shops going in around it.
Good luck and have a safe trip.