Без всяких правок треков и со стандартным фильтром 5м/с
разница в средней максимальной скорости 0,417 км/час :

Андроид:
-> http://www.gps-speedsurfing.com/autoupload.aspx

positional speed, no interpolation
min. speed.: 5knots, max. accel.: 5.0m/s^2

total length: 35.7km, duration 154min

best 10s runs:
1: 12.957knots 23.997km/h [66.7m 10.000s]
2: 12.569knots 23.279km/h [64.7m 10.000s]
3: 12.339knots 22.852km/h [63.5m 10.000s]
4: 11.883knots 22.007km/h [61.1m 10.000s]
5: 11.854knots 21.953km/h [61.0m 10.000s]

average: 12.320knots 22.817km/h

best other runs:
max. speed: 16.600knots 30.743km/h
100m: 12.824 knots 23.750km/h [105.6m 16.000s]
250m: 11.365 knots 21.049km/h [251.4m 43.000s]
500m: 11.078 knots 20.516km/h [501.5m 88.000s]
2s: 14.187 knots 26.275km/h [14.6m 2.000s]
20s: 12.310 knots 22.799km/h [126.7m 20.000s]

Гармин:
-> http://www.gps-speedsurfing.com/autoupload.aspx

positional speed, no interpolation
min. speed.: 5knots, max. accel.: 5.0m/s^2

total length: 35.5km, duration 154min

best 10s runs:
1: 12.692knots 23.506km/h [65.3m 10.000s]
2: 12.242knots 22.673km/h [63.0m 10.000s]
3: 12.002knots 22.227km/h [61.7m 10.000s]
4: 11.823knots 21.896km/h [60.8m 10.000s]
5: 11.668knots 21.609km/h [60.0m 10.000s]

average: 12.085knots 22.382km/h

best other runs:
max. speed: 13.391knots 24.800km/h
100m: 12.401 knots 22.967km/h [102.1m 16.000s]
250m: 11.242 knots 20.821km/h [254.5m 44.000s]
500m: 10.983 knots 20.340km/h [508.5m 90.000s]
1852m: 8.381 knots 15.522km/h [1854.0m 430.000s]
2s: 13.391 knots 24.800km/h [13.8m 2.000s]
20s: 11.906 knots 22.049km/h [122.5m 20.000s]

Да, андроид пишет трек более коряво относительно гармина, но разница в результатах в пределе полукилометра в час.