Unless you have someone inside CX that can tell you preciously the load factor, I would say no. Seat availability, websites like ExpertFlyer, etc. will give you a "general idea", but you never know the exact load factor. I have been upgraded when two nights before departure Expert Flyer shows 9s in Y, and I have seen empty seats when again, research shows 0s all across.

CX are very good with capacity distribution and changing dates just so you *guess* you have a higher chance of upgrade is not worth it in my opinion.