If you're going to follow the coast it's 125.2. If you're going to go as far as Point Mugu remember the restricted and warning areas. Radar coverage is good almost to the surface over the ocean. Point Mugu's radar won't pick you up at low altitude until you're just a few miles from Mugu.
It's been a while since I worked that area but I doubt much has changed regarding sector boundaries.
128.75 is the high altitude frequency for the west side of SOCAL/BUR airspace, 7000' and above (used to top out at 13,000'). Basically it runs from the north boundary of the LA Class B...
Check NTD's operating hours. It used to be 6:00am to 10:00pm but it's been a while since I've been there. I highly reccommend contacting NTD approach on 124.85 for your transit. As mentioned above, if the restricted area is hot you don't even want to think about going around on the warning...