I have my fork cut 40mm longer than the head tube, then I added a 40mm extension. I wanted an almost upright position. I hadn't noticed anything wonky with my steering. Of course, my ride is heavy enough so that it is very stable.

I believe that the stem length issue,. is more a safety issue as opposed to a handling issue. At least that is my understanding, I am willing to take the risk of having the longer stem set up.