We decided to take the old hwy to Half Moon Bay avoiding Devils Slide. It's a fun ride with no traffic (it's closed to cars), but it is much higher and longer, and it has a lot of loose gravel in patches. Due to the gravel and pot holes in the old road the down hill portion was ruined and the ride took much longer than planned. I would not recomend taking this route with road bikes.
Here is the route~