Well a quick try of all B17s at 224 kts instead of 246 max showed the AI overtaking. Also the speed gauge never showed a speed of even 200 mph unless diving!
UPDATE
I am using a 'F' but speed specs for a 'G'
Weights:
Empty: 32,720 lb (14,855 kg)
Normal Loaded: 49,500 lb (22,475 kg)
Maximum Overloaded: 60,000 lb (27,240 kg)
Performance:
Maximum Speed: 295 m.p.h. (472 km/h) at 25,000 ft (7,625m)
Service Ceiling: 35,000 ft (10,670 m)
Normal Range: (normal fuel & max bombs), 1,100 miles(1,760 km) @ 220 mph (352 km/h) @ 25,000 ft (7,625 m)