In my training, I try to do repeats at the same percentage of some of the hills on my upcoming "A" race... but, I typically never do more than 6%. If I do, it is for a very short period of time (<2 mins). I'm sure there is more official guidance from the EN'ers out there.
Comments
* warm up at 1%
* #1 and #4 @ 2%
* #2 and #5 @ 3%
* #3 and #6 @ 4%