A customer arrives at Kirby's Barbeque in Mexia. (Photo ©Chris Wilkins/Texas BBQ Posse) Luckily, we got to Kirby’s Barbeque near Mexia about 11:30 on Friday morning. So, at noon, while the line of lunch customers was building, we were already eating some excellent brisket and some very good ribs. At one point, Posse veteran Bruce Tomaso counted 20 people waiting to order at this rural barbecue outpost about 90 miles south of Dallas. Considering that Big D is roughly 150 times larger than Mexia, population nearly 8,000, Tomaso calculated that an equivalent line at Pecan Lodge would number 3,000. That…