My fastest was on Kanan Dune Road (Santa Monica Mountains) where I hit 60 mph when I was 27 or 28. I also hit 60 mph on the descent of Onyx Summit when I was 50 or 51.
Since then I've hit 50+ (but not much over) several times descending the Santiago side of Cannon, but otherwise haven't found the velocity I need to go faster.
As long as the road is (mostly) straight and smooth, 60 seems to be the limit at which I start to feel like I'm going "fast enough."
Rick / OCRR