mktozd, congratulations!

We were in exactly your situation back in Aug, flying JFK-LAX-SYD. I would review the FlightStats.com and FlightAware.com data on your flights of interest, then give yourself plenty of padding. (We cut it pretty close at 1:20 to secure C upgrades on the transcon, but I also knew that there was a lot of padding built into the transcon flight schedule and also that the transpac leg never left on time either, which ended up being the case on our flight. When we got delayed out of JFK, I didn't sweat it much, knowing exactly how much padding I'd built in.) It depends on the time of year, of course, wrt weather at ORD, but I'd probably be most comfortable with at least a 2 hr layover. You can always hang out at the AC if you are a member or buy daypasses that'll be good at ORD, too.