Considerations of kiln speed and kiln filling degree originate from the days of long kilns where the residence time of the material might be measured in hours. In those cases the impact of a change in feed rate would not be felt in the burning zone for many hours. With a modern precalciner kiln other considerations have to be taken into account. My personal experience is that the kiln speed should be kept at maximum with a precalciner kiln, irrespective of the feed rate. The most important consideration being to combine the free lime formed in the precalciner into the clinker minerals as quickly as possible before the free lime has time to stabilse.