ASSUMING LIGHT TRAFFIC.
70-80 in LA area.
on Freeway 10 and 60, ppl generally drives at the 75-80 range.
on 5 and 110 however, you can't get to such speed without being nervous (poor road condition and cops)
on a unrelated note: me and my roomate once tested our cars' top speed on 710 at midnight.

[not together though]
ODDLY enough,
I just moved to Missouri and found out ppl actually drives FASTER THAN the ppl in LA,.... consider how I drive in LA, I am getting tailgated ALL the time in Springfield, MO. (confused)
on the other hand, when driving thru from Missouri to Memphis, ppl drives SLOW AS HELL... like 70 or under.