I finally got to go down S. Park in Tilden Regional Park when it was closed to traffic - steep and fast! My computer was out, so I'm not sure how fast I was going. Only a couple of people walking dogs, and no salamanders were hurt on the run. There's a stop sign at the bottom, but it seemed to flatten out and you can see it coming from at least a quarter mile away.
Another oldie but goodie is Palomares going South to North (ie, from Niles Canyon to Castro Valley). Not super steep, but long enough and straight enough to get up close to 50 without trying.
JB