I am 5'9" myself and I got the small originally. If it were summer all the time or I had $$$ to buy different setups, I would keep it. But at the price point, $149 I am going with the 14 oz regular over the 9 oz small.
It is winter in TX and I find that I wake up chilled or cold from my feet being on the ground. I do honestly feel a little uncomfortable though from the shortness of the pad. I have tried to put my pack or anything under my feet, but I just have not found anything that works. And even if I was going on the AT, I would still not even be carrying enough clothes to put under my feet! :D
So, IMO, I am going with the 72" version to have a truly beautiful nights rest on the trail. After all, a good nights rest makes hiking all day that much easier/better.
Hope that helps.