At least for the Holux GPSport 245 device the logged speed is not at the same position and not in the same format as other device.
For this device the SPEED is not logged after the HEIGHT but just before it. And it is not a float in km/h but a long integer in cm/s.
I've made the following patch and verified the gpx output against another mktbabel device output (an iBlue747 A+).
In this patch I've presumed that other Holux device have the same logging schema, but this need to be checked.