I'm 5'6 and normal weight, I did a standard flight from EU->San Francisco and on the return when checking in I bought pretty much any update that was available to give me more leg room/space. I swear I will never do another 5+ hour flight that isnt at least business class. I had back pain for a month. My feet were swollen for a whole week that my shoes didn't confortably fit, etc that I will easily lose a paying gig over doing a flight like that ever again.