As an 1K out of LAX/SNA, my upgrade rate has been 100% (knock on wood). Yup, 100% and out of LAX no less. Maybe I am lucky, or maybe I pick the right dates. I have cleared on some of the toughest routes:

LAX-BOS/JFK/HNL/ORD/DEN-LAX

Of course, I also take advantage of neighboring airports like SNA, and I also request my upgrades immediately after I purchase my tickets. I've had 1K agents telling me that F is oversold an I would never clear. However, when I go to the airport the next day, they have a F bp waiting for me