I actually disagree with this. From tests that I did the slowest data rate performs very bad on a mobile node. The best reason I can think of is that you get fading of the link as you move, and therefore long sequences of bit erasures with which the forward error correction can not deal. I'd rather send 10 packets at the fastest data rate, than one at the slowest. The short moment that you have a good link at least you'll get one full packet through.
My test setup is an Arduino + RN2483 at data rate 5 (sf7), power 14dBm. Source code on my github page, results on http://jpmeijers.com/ttnmapper/kml