Not that I am necessarily predisposed towards the theory of shock cooling, I think that to compare the temp drop immediately after shutdown does not compare to the temp drop when the cylinder is at operating temp. Maybe 400 deg or more. The cylinder is much more highly stressed at this temp than it ever will be at 200 deg and losing 100 deg in 30 seconds. Still, we use a simple system of cooling, works well for planning and the flight and is theoretically gentle in cooling. We get good cylinder life, so who really knows.......