I was cycling up those hills mostly in sitting position. On longer hills it gets pretty monotonic, mentally tiring and would get me all stiff. So bit by bit I would start to climb out of saddle. In the beginning I'd grossly misjudge my efforts and blow up pretty soon. Then I would have to sit and my overall speed would drop big time. But over the time I've learned how to pace and now it does not matter much. I can go either sitting or out of saddle for an hour. The average power in case of out of saddle is just a bit higher with the same perceived efforts (my out of saddle cadence is very low). What I did noticed though going out of saddle has greatly increased my hiking abilities. I cycle whole year but I only hike very short time in the summer. So when the summer starts and I go hiking I would be completely out of shape. No longer the case.