Thank you everyone! I did it and it was awesome! Incredible views and great way to spend a day.
Finally I chose the San Pedro Mountain Road and HWY-1 all the way down to Santa Cruz.

San Pedro Mnt Rd was a really interesting part because I haven't done any mountain biking before. Well just like you said it was tricky on a road bike especially downhill. Although the view was amazing! I'd say - just to stick with the original topic title - that HWY-1 is probably safer through the tunnel on a road bike. Also it's much-much faster. I recommend to start the ride early to beat traffic.

After San Pedro Mnt Rd, HWY-1 had pretty good biking conditions, huge shoulders everywhere. Someone in an other thread mentioned that HWY-1 is flat all the way down to Santa Cruz. Just a word of caution for absolute beginners like me: it has numerous 5-6% ascends and those can easily add up.

Also it's worth to plan carefully where you want to stop for a brunch or a beer, because south to Half Moon Bay the options are pretty limited.

All-in-all I think this ride is gorgeous and I can recommend for everybody who did 50-mile+ rides before.