Originally Posted by AZBuck
Depending on your driving habits, mostly how many hours per day you are comfortable driving, staying 'farther south' would add as much as half a day to your trip. That would be from roughly three-and-a-half days to four, which you might find acceptable. However, there is no guarantee that such a route would mean no snow or ice. Indeed, if there is any frozen precipitation on a southern route, those areas would be far less prepared and equipped to handle such weather. To be fair, first priority usually goes to keeping the Interstates open, but still that's a lot of roadway to plow and/or salt. And if they salt, you may not want to drive your new(?) Porsche on such roads. Then there's the fact that you have to end up in St. Louis no matter what, and that's where your chance of snow or ice is greatest.
All of the above is to say that there are many factors that go into the decision you'll have to make, some of which you won't know until just before you set out on the drive. If you do decide to stay south, I wouldn't use I-40 which gets to significant elevations in sections, but rather I-10 to west Texas, I-20 to Dallas/Fort Worth, I-30 to Little Rock, I-40 to (almost) Memphis, and finally I-55 to the St. Louis area. Note that while there may be shorter routes that remain that far south, the stated route is all Interstate, and can be done in four days at a little over 500 miles per day. But I'd schedule five days if at all possible just in case you need to sit out some bad road conditions. Also, I would not make lodging reservations, leaving where to stop each night up to the weather and your own comfort level.