I do not know how true the film info is, but Target for Today mentioned group climb as 150mph, 100ft/min and later after bombing, lead straight for 15 sec, then turn to rally point, speed 155 ias, making s turns for others to catch up.
Memphis Belle mentioned climb 300ft/min after 10000ft.
How to Fly the Boeing B-17 "Flying Fortress" - Flight Procedures (Restored 1943) mentiones speed 150 ias and power used for normal cruise is depending on flight conditions- desired range, fuel available, weather conditions, altitude, gross weight etc. Pilot`s operating handbook should have graphical tabels to find performance data and power settings. Like distance travelled to reach target altitude at certain gross weight etc.
Ground speed depends on wind as well.