A couple of screenshots from google-earth. These are GPX files exported from my own Garmin 910xt and my friend's Suunto Ambit.
The 910xt was set on "smart recording", while the Ambit was set to record every second. Both watches are quite confused in tunnels or under bridges. It's clear that the garmin-trace is somehow filtered. A better comparison would perhaps be to set the 910xt also on 1s-interval recording.