I assume your coming from Northern Cali.
For the most part its 70 mph (from salinas to about Atascadero) after which is 65..
those are posted speed limits. Be careful around KING CITY.. its CHP headquarters I believe.. or whatever they have a huge CHP thing there.
For the most part traffic runs between 70 and 80mph...
for 180 miles give yourself about 3 hrs .. you might get a bit bogged at the Cuesta Grade.
Im going to be in San Luis Obispo this weekend.. my friend lives there..

glad your joining Calpoly, its a good school, lots of beautiful women and handsome guys. My friends brother is still doing his schooling there.
There is not much to do there, but what's present is plenty..
Edit:
Since your leaving in the morning.. be prepared to see these buses with a porta potty trailing behind.. atleast that's what I saw when i went that way early morning in may.
Farm workers being bussed to work. They can be a bitch to over take despite it being a 4 lane highway (2 lanes per side)
edit: be ready to slow down near salinas/monterey speed limit suddenly drops to 25 in a school zone from 55mph.