We have a winner :) I timed it too out of curiousity. It was about 1 minute faster to take 580 to 680 than it was to take 84 and get back on 580 at Airport. That was towing the boat with absolutely no traffic (14 minutes 580 to 680 and 15 minutes on 84).

I don't know why I put this post up really, other than that I always had wondered which was really faster and I've had people tell me both ways are faster than the other. I do know if you're headed toward the bay on a Saturday or Sunday afternoon, taking 84 can be a lot faster when 580 backs up.