nice and exhausting day, did 40 runs but started to change my set-up too late, anyway a good day. Used four differnt GPS-units for comparison (GW52 at 5Hz, GPSLogIt on a Samsung Galaxy J1):

                      max    10s      5x10s   500m
GT31            40.74   40.13   39.84   39.31
GW52           41.11   40.16   39.85   39.33
GPSLogIt      41.19   40.32   39.90   39.40
Ambit3          41.06   40.39   40.13   39.62