For a simple, pure-speed run try Evora Rd going east toward Pittsburg/Baypoint in Contra Costa.
From the top of the Willow Pass Grade on down.
I hit 53.2 MPH down that on Saturday. It is so long and straight it is like cycling down a ski run.
Pavement is really nice eastbound. Climb it from the west, descend it headed East.
The pavement on the climb side (West Side) is not so hot. I would not descend that direction plus the sun would be in your eyes.