Need more info first. what kind of altitudes/temps, stage length, lake/river/ocean. docking areas. ad nauseum infinitum. The otter is a superior float aircraft, tougher, shorter takeoff, lower stall. figure a 3500# payload on amphibs. 9 pax+bags @ 225 per figure 1400# fuel with full load. so 2+30 and reserves. if you have a really long stage length then the van will be faster, but fuel/overhaul/maintenance must also be considered