The last few times I've flown US-SYD, there have been 12-15 people trying to upgrade to 1-2 seats in both C and F. That was on the 747s in Jan and March. The 777s have fewer seats, making it even worse.
I'd say your chances of an upgrade as UA 1P on a flight that's already C1-3 are close to zero. C1-3 could mean that the flight is already overbooked, although they are still willing to sell full fare tickets.
Good news is the 777s are much better in economy than the old 747s were. Flew them yesterday SFO-SYD and was pleasantly surprised. Very light load: most passengers in E+ got a row of 3 seats
