I had a fairly insane experience with this.
I'd made a berserker on the same account as my enchanter, but quickly came to miss the enchanter and abandoned the zerker at level 94. With the chanter maxed for AA, I decided to dust off the zerker after months of not playing, but sharing had always been on.
It was insane. With lesson I was getting 6% regular exp per kill. With the SC potions, 4%. I blasted to 102 in a day. Then, sadly, the gravy train ended. I went from getting 2.7% per kill to 0.3% per kill in one fell swoop at 102.
Man I miss that.