Whew. You may just "stroke out" in the panhandle in July!
Not that we aren't already doing so here!
Dallas would be way out of the way. The route through Abilene is not too bad, we've come back that way - through Brownwood and such on 183.
Which side of Austin will you be coming from? If you're in South Austin, I'd recommend 71 west to 281, then north through Marble Falls to Burnet, and pick up 183 there. North, I'd just say 183 to Brownwood, and then pick up I-20 to Abilene, then north out of Abilene through Lubbock. Pretty much the straightest shot, good highways, too. Figure on an entire day of driving though. Good lunch place in Brownwood called Humphrey Pete's, with room to park nearby. There isn't a whole lot to see out that way, and what there is may be pretty crispy by next month, I'm afraid.
We'll be heading out first weekend in July to Ft. Davis ourselves. Hopefully a little cooler out by the observatory.