My deal with standing is that for some reason it would torque my left knee (before I went clipless). Hills that I would be painfree on if I sat and pedaled were suddenly stressing out that knee and I'd need a week to recover. Had basically written off standing up hills. Part of my reason for standing was I wanted to be able to go faster up the hills, and sometimes it was because I was too tired to try to sit and pedal/wait to get up them... Odd, I know. And it makes no sense to me as I write this... These are all types of hills: long ones, short and steep ones, long and steep ones... No matter, if I stood up it, I paid for it. Since I got the clipless I am hoping that it keeps my knee more stable and I can go up the hills easier. Aerobic fitness? Still trying to regain that. So for me right now it is the easiest gears all the way up, baby. At the top of the hill I collapse in a pile until my breathing recovers, and then I keep going. Fun stuff.