I do hill repeats on anything from 3-12% - depends on what I'm trying to work on. I have a few 3% grades that I try to go up as fast as I can and keep my speed up pretty high. Then I have a hill that is so steep that I can only do it once and my gola is just to get up it without stopping. The main one I do is just around the corner from home. It's about .5km long and about 6-9%. I time myself and do it about 6 times.