A number of pitmasters suggest smoking low and slow at 225°. I've tried smoking at that temp but for me it just takes too long. You said that at that temp your St. Louis ribs after 5 hours were still underdone. My favorite temp range is 235-242°. I say "range" because in my MES 30, which is over 4 hours old and has a new controller, the controller will cycle a few degrees above and below the set point until about 5-6 hours in the temp remains stable. But my point is at that 235-242 range I can finish off two racks of STL ribs within 5 hours. At 6 hours the meat is too much "falling off the bone". To me, if a pitmaster is in a competition and has all day or night to cook up ribs, brisket or whatever, they can afford to keep the temp down at 225°. I have a beginner's smoker cookbook by Ray"Dr. BBQ" Lampe and he instructs the set point to be 235° for just about all the recipes. That temp range has worked fine for me.
Everyone is different. I am close to Rick @ 235-245 degrees. I will have to check, but I think I read in Arron Franklin's book that his temp is 275 degrees. We need to keep in mind though that we are using electric smokers and Aaron and other pitmasters use wood and a complete different type smoker.