Run with Vivoactive HR vs Fenix 5x in Osaka, Japan. You can see that both runs show same distance on mygpsfiles.com but on watch the 5X recorded 6.59 and Vivoactive closer to actual distance was 6.67. Track on Vivoactive HR definitely better as well! I have found that the 5X clips about .02 miles off per mile. Doesnt sound like a lot unless you are running long distance. On my 50 miler two weeks ago almost added up to an entire mile off by the end of the race.
Fenix 5x track is in Blue, VAHR in Orange:
http://mygpsfiles.com/app/#4h68bEDV