I've done Riverside - Jarupa Valley - Chino Hills - Harbor Blvd to PCH a couple of times now since asking my orginal question.
It's good in that you can bale and jump on a train at several points in case of heat or something, but Harbor sucks, in fact the whole Chino Hills - PCH section of the ride sucks, too many stop lights and too much traffic. To the point where I called and got picked up by Disney one time (84m in so I didn't feel bad about it) as I didn't want to deal with it any more. Through to Chino Hills I averaged 22.8mph without really trying, thanks to the route being gently downhill most of the way. Tha'ts a real nice section of the ride.
I'm wondering though, is there maybe a bike route to PCH, along a river or freeway? If so where from/to? I'd be happier finding something like that.
Thanks for the replies!