I love my Blackvue dr500gw-hd. Video quality, frame rate, build quality. GPS-based speed calculation is solid enough. Accelerometer is pretty fast without being too twitchy. No complaints yet.
I haven't used the WiFi option yet, but the "event driven" recording is a worthwhile feature. It makes perfect autocross videos automatically, and the software is solid enough.
When I was reviewing the tech, this place was an awesome resource:
Dashboard Camera Reviews
Sample of me driving slow:
[ame="https://www.youtube.com/watch?v=lLioOy9apfQ&list=UUgc5KArZ3_-VzWFnNir2M9w"]Run 6, Pt 1 - NER SCCA - August 2013 - Devens-Moore Airfield - YouTube[/ame]