I would also point out the single engine service ceiling figure is based on the airplane being in a clean configuration, critical engine inop, prop feathered, at gross weight. This last item is critical. I have just under 1900 lbs of useful load. Whenever I am going over the Divide I keep the plane light; it is never anywhere near gross. Thus actual single engine service ceiling is thousands of feet higher than the published at gross weight figure (the Aztec has a chart in the POH to calculate it).