I've been using Navigator with HD Traffic along side TOMTOM with live traffic.
TOMTOM will sudgest a faster route when it is 2 minutes or more quicker.
When does Navigator decide to reroute?
On one occasion TOMTOM sudgested a route 20 minutes quicker avoiding a 30 minute delay. Navigator was aware of the delay but only change the route when I asked it to recalculate.