I find the scrolling method to be quicker.Instead of using the scroll wheel you can either touch (and briefly hold) the speed sign on the touch screen or hold the drive stalk down for a short while.
This will set the cruise speed to the detected speed limit.
But the auto detection was way better. If it speed reduced automatically on entry into a town it would also increase speed again automatically, when exiting the zone (Think passing through a 1 horse town in the country). The odd thing was that if you activated Autosteer in a towns 60 zone it would not auto increase leaving town at the 100 sign. You would need to spin or tap the 100. Needed to reduce speed in autosteer first.