Coming down from Tulsa, headed toward Houston, I almost always go straight through Dallas on US-75 to I-45. My usual arrival time, southbound, will be around noon to 2 PM, and traffic is usually pretty good, the worst of it usually being McKinney to Richardson, where there is a lot of local traffic. Downtown is usually better, as local traffic is better separated from through traffic.
I have alternative routes to Houston (through Palestine) and another to San Antonio (through Wichita Falls) that bypass Dallas, but my route to San Antonio (for you would be I-40 to I-44 to US-281) is a few hours slower than I-35, assuming no major problems on I-35. There is a more direct route from Wichita Falls to Boerne using US-87 but having not tried it, can't recommend it.