A bigger factor then RW slope are obstacles in the departure corridor. They can have a huge effect on runway allowable weight. As far as taxi speeds you noted the two extremes. I have seen several taxi way incidents with SWA. Sooner or later they will have a serious one and slow down. If you have a incident and are going faster then the Boeing book speeds you can expect lots of trouble from the FAA. 30 knots on a straitaway, 15 knots on turns less then 90 and 10 knots on 90 degree or more turns.