Well if you are going to take most of the day to drive anyways, I would consider doing both the 5 and the 101.
I'd take the 5 to Kettleman City and go west on the 41, which takes you to the 46, which then hits the 101. Maybe sounds confusing, but if you look on a map, it's pretty easy.
Going this way will take you through the beautiful wine country of Paso Robles, the beaches, Santa Barbara, and so on until you hit the 5 once again. And if you have some more time, off of the 101, there is a darling Danish town called Solvang. Lots of windmills and gingerbread buildings to see.
Anyways, if you time it right, for lunch, you can either eat at the Kettleman off-ramp at "In and Out Burger" or go to our favorite place to eat in Pismo Beach called "Splash Cafe" right up the street from the Pier. They serve the BEST clam chowder bowls, or burgers. Very well known place, and the line could wrap around building.
But it's fun and good. If time allows, Pismo is one of the very few beaches you can take your car out on it for a drive.
Have fun!