Guardians is now out everywhere, except Japan (which doesnt matter much). It has also been out for two weekends in many of the bigger overseas territories. With only $283M to date, $500M overseas is probably not going to happen. Maybe $450M or so.
Domestically, this weekend puts the domestic total at $325M on the "no legs" end of things and probably $375M on the high end. I would guess $350M for now.
So realistically, $800M is a lot more likely than even $900M. $1B would require this to not act like a comic book sequel at all, and for Europe to suddenly develop an overwhelming urge to repeat watch starting next weekend.