I used to always go I-5 if I was in a hurry. The word is out. These days, my route is a game time decision based on traffic. I check the traffic apps and look for the route with the best traffic flow. I have seen I-5 in total gridlock, as well as 99. As you get closer to Stockton on 99, the traffic almost always starts thickening up. In that case, jump on 4 to I-5. But again, it is variable from day to day.