I can say that the general consensus for PMUA flights is that ORD/SFO-HKG flights are in the top two or three most difficult routes to upgrade (HKG, SYD and SFO-FRA all vie for top honors).
Having said that, your date does look pretty open from either EWR or ORD. I would probably take the non-stop given that it eliminates the chance for your upgrade to clear, only to mis-connect.
Of course, the higher the booking class the better the shot. So if you are forced to buy M or above, given the current load I wouldn't be too nervous.