It is common for the Pacific High to be amorphous and north at the end of June / start of July, then to move south and become more focused by mid-July. There are plenty of exceptions to this though, including last year when the best route
from San Francisco to Oahu was actually north of the great circle route
I've sailed back to San Francisco four times now, each time in late July or August, going over the top of the high as best I could. It's taken me between 17 and 19 days, and I have had to sail as far north as 42 degrees N. I've also been able to keep my northing to 39 degrees, and I only went that far north to ensure I had a favorable angle on the wind and seas as I transited the "squash zone" on my final approach to the mainland. Here are the tracks of my Hawaii trips:
The track just north of the great circle is my 2010 "to Hawaii" path. Everything north of that is a return track.
Bottom line, the Pacific High moves around a lot, and when it is diffuse (often the case) it can be very unpredictable with no real center. At these times the low pressure systems moving down from the Aleutians can be the determining factor in when you make your turn to the east.
I've had friends sail under the high, usually because they were heading for Los Angeles, but also heading for San Francisco. They usually get beaten up worse than I on out northern route, and I often get to San Francisco just as fast as them.
Finally, do look at the coastal gales you are likely to encounter as you get within a few hundred miles of the mainland north of San Francisco. These can be quite bad, although the odds are definitely in favor of having a pleasant trip.