OK, a little blast from the past. I grew up in the DFW area and remember listening to WBAP's old Bill Mack overnight show in the '70s. One time, maybe around 1972-73 or so, he read out a postcard he had received from a US G.I. radio operator in Guam that had picked up WBAP's signal one day (and quite clear, too!). I make that at about 7200 miles.
On a related note, from what I remember from my DFW days, WBAP had a horrible "dead zone" at night in between the ground wave zone and the sky wave zone. It was like a donut-shaped area from about 50 mi. out to roughly 150 mi. It did vary considerably with seasons and weather conditions. I remember it always used to drive my Father nuts when we were coming back home from Central Texas late at night. He would eventually give up on WBAP and settle on WHO which came in great all the way home.