Here is a trick we learned for drives with heavy traffic. Once you pass Magic Mountain watch for the 210. Take it east to the 605, take the 605 south (get in the HOV lane) to the 91 EAST, get in the HOV lane, and get back on the 5. If there is no traffic on the 5, my route will take you 20 mins longer, but if it is during rush hour, we have saved an hour (had my sister go down the 5 to compare.)
This way works good if you don't get stuck on the 210 leaving Pasadena. The section from 134 to the 605 is frequently backed up during the evening rush hour. Of course it is usually better than I-5 through downtown LA.