very true that S. CA temps will well be above those of the "Sunshine State" as far as true air temps and I don't know what if anything humidity has on the A/C system. I am going only by experience with duracool here. I know that it keeps me cool here and will about freeze me out of the car when it's in the low 80's.
You said you wanted to convert to 134 and as many have said it is not a good idea with these cars. Trust me it does NOT work in FL. daytime May through October and would be just as bad in S Ca. Keep your car r12 or at least look at the alternitives on the market. 134 runs at pressures your A/C system was NOT designed for and will result in premature faliure. If my cars had not been converted to 134 using PAG oil I would use r12. Now the hassle of flushing and replacement of key parts keeps me either running 134 or duracool.