Both very helpful responses. Thank you.
I am checking on Swiss prices vs trains from Stuttgart as we speak. Then again the rate may be better from Frankfurt.

One small update: In order to catch DL 27 FRA-ATL, I would have to us an LX flight that runs 7 - 8:15 am and Delta 27 leaves at 9:45 am. Given that FRA is such a large airport, is this enough time to catch the Delta flight?
On the other hand, the STR flights work well as you have them. Thanks ClipperDelta.