Check out the Texas gardener magazine. They had an article regarding tomatoes that I found useful. Its packed at the moment, but I now our lbrary carries it!

I'm from San Antonio and currently live in Lewisville, which is north of Dallas. I'm not sure that "large" tomatoes really like our climate. I haven't had any luck with them here and remember limited (not even fist-sized) luck with them in San Antonio. I'm starting to think that we're too far south (get too "hot" too soon) for the larger (slicing) tomatoes. But, I've had good luck with the "Sweet 100s" and all of the cherry tomatoes in both locations. So, unfortunately, I'm afraid we really can't grow the big "beefsteak" tomatoes, but we can grow tons of the cherry tomatoes!