so here is my advice and take it for what it is worth.
Day 1 I-5 as mention, WILL BE DAMM BORING!!! but it is all the time you have, camp in Mt. Shasta area. (668.7 miles)
Day 2 go back a little south to Redding and take hwy 299 to the coast and then north on 101 all the way pass Redwood N.P and continue along the Oregon Coast until Hwy 38 and make a right and the I5 and you will be in Eugene (461 Miles)
Day 3-4 Eugene
Day 5 Eugene to San Francisco Area on I5 (528 miles)
Day 6 1 and 101 south San Diego This one is a long ride so maybe you will to go a little bit farther south the day before (maybe Salinas) (577 miles)
I did the calculating with Microsoft street and trips for times and distance. as you can see it does not leave a lot of time for smelling the flowers, but it can work...
A motorcycle or scooter always turn a bad day into a great time!
KLR 650, Honda Beat scooter!!