According to Wikipedia, Flyer II and III had the same max. speed, 35 mph, but for some mysterious unknown reasons Flyer III had a much poorer weight to power ratio
1)
Flyer I 1903 (see:
Wright Flyer - Wikipedia, the free encyclopedia )
Max. takeoff weight: 745 lb
Powerplant: 1 × straight-4 water-cooled piston engine, 12 hp
Maximum speed: 30 mph
Weight/Power at 30 mph = 62 lb/hp
2)
Flyer II 1904 (see:
Wright Flyer II - Wikipedia, the free encyclopedia )
Loaded weight: 925 lb
Powerplant: 1 × water-cooled straight-4 piston engine, 15 hp
Maximum speed: 35 mph (56 km/h)
* Weight/Power at 35 mph = 62 lb/hp
Wilbur in Flyer II Circling Huffman Prairie November 1904. The front elevator has been enlarged & the radiator moved to a rear strut since the May photo above.
3)
Flyer III 1905 (see:
Wright Flyer III - Wikipedia, the free encyclopedia )
Max. takeoff weight: 710 lb
Powerplant: 1 × Wrights' water-cooled, 4-cylinder, inline engine, 20 hp
Maximum speed: 35 mph (56 km/h)
* Weight/Power at 35 mph = 35.5 lb/hp
The Wright Flyer III over Huffman Prairie, October 4, 1905, Orville piloting.
4)
Wright Model A 1908 (see:
http://en.wikipedia.or/wiki/Wright_Model_A )
Loaded weight: 1,263 lb (573 kg)
Powerplant: 1 pusher × Wright Model 4, 35 hp
Maximum speed: 42 mph (67.6 km/h)
Weight/Power at 42 mph = 36 lb/hp