I was hoping someone closer to your climate would be able to answer this for you, since I have never gardened in Texas or any place similar.

That said, I don't think any of the perennial geranium forms do well in prolonged heat. We had extended heat and drought last summer (week after week in the 90s and sometimes above 100) and all of my geraniums looked unhappy. True, they were newly planted that spring but, even with attention to supplemental water, many died, stopped growing and/or shriveled in size. Some of them came back and had a bit of a second wind when temperatures finally moderated in September and October.

Of all of them, 'Rozanne' was the only geranium that tried to bloom during the heat. It didn't grow hardly at all but still kept producing a small quantity of blooms. Heat makes the blooms on this cultivar become tiny, washed out and pinky in tone. In cooler weather, they are much larger and fuller and can approach a true irridescent blue color. If you can provide some afternoon shade and regular water, this one might work for you.

I find in general that any plant sold by Plant Delights Nursery in North Carolina will have good heat tolerance. They list 'Rozanne' along with several other geraniums.

I am in South Ga and have great luck with ballerina! We get the heat like you and mine were tucked under shrubs. They got full sun most of the day (including afternoon) I really had to baby them the first year, but the next year they plugged on. Bloomed great and had good fall color. Love them.