Can't really comment on the hills since I only ride flats. But I do know when I first started riding, my normal-high cadence was about 80-85 at higher speeds (or what I thought was high speed). And now, when riding at higher speeds, I sometimes feel like I'm mashing when I'm really just spinning at 90-95. I like spinning around 100 but there are times that I really enjoy that "mashing" feeling at 90 rpm. Especially when pulling, I like to push a harder gear. I feel with time you will find out what works best for you and what doesn't. Look around at how others are spinning around you to get a general feel as to how you should, and then just adapt to what you like.