Did some tests at the Rudskogen track this weekend.
Looks like you get a lot better results when you use a bluetooth GPS versus a integrated one. The Google Earth overlay are a lot more precise and equal with the external, and the graphs are much smoother as well. So it will be external with a good placement for me in the future.
Will also try to compare a 5 Hz to my 1 Hz pretty soon and guess I will go for one of those.