Light traffic: 80mph
Medium traffic and heavy traffic: speed of traffic. During medium traffic I'll tend to go around 70 in the left lane as that's what almost everyone in that lane travels at.
I just got back from Disneyland, live in Bay Area, and it was mostly around 80-90. Took me exactly 5:30 hours to get from Disney to my house.
Also, people who slow down like crazy on the freeway when they see a cop piss me off. Shit is always a close call for people behind the first couple of cars that see the cop. Going from 70 to 45 on the freeway so fast is a hazard.