Okay, I can't speak as to whether fare class trumps status or vice versa, but I can definitely offer significant anecdotal experience that fare class DOES matter. I am SE, my spouse is E. When either of us travels on a Tango Plus M fare (the highest fare class in Tango Plus), our upgrade success is very very good. Like almost always with just a few exceptions. This is at the 7-day window, clearing before day of flight, and at the gate. Other Tango Plus fare classes, I still don't do too badly, but he rarely gets the upgrade. So both factors (status and fare class) are definitely in play; I just don't know what the actual algorithm is!