We thought more along the lines of Doogie Howser or a 3 year old that knows all the states and capitals or can tell you everything about every dinosaur that roamed the Earth.
While not Doogie Howser, my 3/4yo did know all the states and capitals and could tell you everything about zillions of ocean creatures. I don't think he will test much above 140 (just basing this on comparison with his sister and where she tested).
Some kids are just more into the whole "knowledge sponge" thing, I think.
He still has time to become the next Doogie if he wants to!
I totally agree about the sponge thing. All those incessant, infernal questions they ask us about all the time - they actually absorb and recall the answers. Ahhhmazing! LOL!
You probably understood that him knowing all those things is unusual, since you had his older sister to compare to, right? That helps you come up with the 140ish estimate. What did you know about giftedness prior to your daughter?