If you're going to be putting adults in the third row, the Model X
might be for you, and the Model 3 won't be.
That said, with a squared off back end, a Cd of 0.30 would be doing good, and that would cause a
considerable hit to range most likely. By "considerable", I mean, I wouldn't be surprised by, on a Dual Motor car, something on the order of 230 miles range.
Playing with them some more, I must have introduced some of my own error.
Having scaled the Model Y's front wheel appropriately, I'm now getting 633.2 px wheelbase, which would imply 2966 mm... one mm more than the Model X. (And, there's still a lot of error possible in this method, so...)
This thing is definitely longer than a Model 3, no matter what...
And, also, here's some unibody structure images to compare:
Model 3:
Model Y: