Good speculation, Wunwing. Another factor to consider is what range that aircraft will have with loads that are significantly heavier than the passenger equivalent. this aircraft is an ER but I don't know if it is certified to the same MBRW as the pax aircraft (412.7t). The Atlas B747-400F aircraft have a MBRW of 394.6t whereas the pax aircraft operate up to 397.2 (I believe that is because of loading limitations to stay within CofG limits) and there is no tail fuel tank fitted to those aircraft (I don't know about the ERF). So with higher payloads, reduced fuel capacity & reduced MBRW, the tours of duty may be less.