[walrus01]

The exact likelihood of being able to max out your lan side 1GbE interface to a home gpon terminal also depends on some factors you can't know unless you are the ISP, such as the usage patterns and traffic volumes moved by your neighbours on the same port. Could be wildly different if you happen to be in a condo with some person that is seeding popular torrents or if you're in a neighborhood of mostly retirees for instance.

Not sure what you mean by at worst a 1:2 split since GPON last mile can be implemented at the physical fiber level as many possible configurations such as a 8:1, 16:1, 32:1 split. Your ISP isn't likely to tell you or share with you the optical link budget and split of your segment.