I've now had several sessions with the Garmin (F3) side-by-side with the GT31 and so far the F3 is consistently slower and records less distance, but not by much. When sailing this week the GT31 recorded a PB whereas the F3 didn't. Glad I had the GT31 and I will continue to wear it, but I love the feedback I get from the F3 and for every day sessions I probably won't bother pulling the memory card out of the GT31 for KA72 upload when the F3 does it wirelessly as soon as I walk in the front door

As an example, here's the stats from my last session:

GT31
2 Sec Max: 37.497
5x10: 35.009
HR: 16.017
Alpha: 21.292
Nm: 24.545
Distance: 107.064

Garmin F3
2 Sec Max: 36.973
5x10: 34.679
HR: 15.777
Alpha: 21.264
Nm: 24.114
Distance: 104.851

Apart from the use for windsurfing, I just love the F3 for pool swimming and especially for soft sand training as it's got great settings for configuring fartlek and interval sessions. Plus all the other statistics a runner needs.