On a slow Sunday afternoon I asked the controllers if they had time for me to take my M20E to 21,000 feet. They said sure, think it will make it? I wondered that myself. I made the trip from Dallas to Memphis weekly. I was able to make it to 21K, but it probably took 10 minutes to get that last 1,000 feet. I stayed at 21K for about ten minutes and then asked for lower. The manifold pressure was very low, I will need to see if logged it in my logbook. The thing I remember most was the lack of controll. It was extremely mushy and a little frightening. They list a service ceiling of 21K for the E model. Technically, I hit the service ceiling at 20K or less (100 fps climb rate), but it made it to 21K. I seriously doubt I will ever do it again.
I commonly fly 9 to 13,000 feet on longer cross countries with the E model, if there are good winds. On shorter trips, I normally stay at 9 or less.