The following link to a thread on the Lawn Care Forum includes a ranking based on drought recovery for a number of Texas lawn options. No source given, but info seems to fit with other references I've seen. Floratam gives best drought performance among St. Augustine choices. Though while it may survive in zone 7, it's usually not sold there because not considered reliably cold hardy on the north side of 8. Palmetto is probably the best colder hardy SA for shade and appears to have better drought performance than Raleigh SA, but not much independent study/test info on this variety at this point.

Raleigh has been the "standard" SA recommendation in north Texas for years because of its cold hardiness and disease (SAD) resistance, but we've found it hard to keep healthy on a single weekly deep watering in some full sun areas. We've been patching Palmetto into these trouble spots, but haven't lived with it long enough to judge it's drought performance. However, it does seem to be thriving in heavy shade where the Raleigh was in decline.

Here is a link that might be useful: Thread on Empire Zoysia vs Floratam St Augustine

This post was edited by bostedo on Mon, May 13, 13 at 14:47

Thank you, I am off to read it!