SFO is a tough route IMO if going hub to hub. I usually fly SFO / ORD 1-2 times a month. I've had 0 upgrades this year out of 7 flights departing SFO and only 1 upgrade on the 5 flights departing ORD to SFO. So about 14% for me for a SFO departure.

The flight from two weeks ago, SFO - ORD was a M fare and I was #14 on the list. Usually if going out to SFO, I get there mid-week and depart SFO on a Friday.