The hotter the better, yes, even in Texas. Keep in mind that a 188 t-stat is open just as wide at 200-plus degrees as a 168 t-stat, so therefore a 168 should have no advantage when it comes to preventing overheating. Also, with non-sleeved Fords (i.e. no liners with o-rings), you don't really need to get worried until the coolant temps approach 250 degrees.
Engines run better when they're warm, use less fuel, and boil water/condensation out of the oil easier also.