Whoa, I just looked it up. The max elevation for Belgium is 697m or 2287 feet. That's like doing a local climb in my neighborhood! 
Yeah, and that 697m is far from where I live

When we have 500m of height difference in a ride it has been fairly hilly for us. Anything above 1000m on one ride is quite a lot and comes with 100km+ of riding

But the ride I did Saturday was a gravel ride. And since we don't have a lot of gravel here, it is a lot of twisting and turning in the (small patches of) forests and singletracks, so I did use my brakes sometimes. But never more that a couple of seconds at a time, so I have no idea how they perform on longer descends.
But on the whole ride I did not once think about the new discs (good or bad), so I guess they were OK.