GPS is interesting to know where you are but the speed/distance accuracy is not very good especially the speed.
So the speed and distance from the HxM will be very usefull because the speed given by the GPS is very inaccurate.
I hope you will implement and dump !! in the csv the two fields coming from the HxM not currently used : HxM speed and HxM distance.
it would be nice as a first step (before using them to correct GPS info) to at leat dump in the csv file all the info coming from the HxM (speed, distance, 3D acceleromter).