Is that with or without the trailer Mooch? I'm not sure I've seen over 6 kph on downhills, including the steep section coming down the Gateway bridge. 6kph is still more than enough to get pinged here in Aus.Oh sure it does eventually pull back to the set speed but it takes way longer than it should after you hit the level. I go over a steep incline/decline bridge with an 80km/h limit and if I set the ACC to 80, I'll be doing 88 within a few meters of hitting the peak of the bridge. At the bottom of the other side it levels out and heads around a bend and there is often a copper with a hairdryer around that bend. Unless I intervene, the car will still be doing 85/86 a good 100m after levelling out.
It gets about 5kph over constantly around the hills where we live, so yeah, you always need to intervene.