This thread is a wall of text for me right this minute. (See time of post) But I did read the first three or so posts and can see that you are equipped and financed for such a trip.

From Boston I don't know how you would route it but I highly recommend this venture and that you get yourself to the old Route 66 asap from your start point. I may have missed the post where you said you were going to give the vehicles away on the west coast but if you intend to return then you should take a northern route west then a Southern route home, or vice versa.

I've done the cross country drive as far as Window Rock, AZ and enjoyed it but our purpose then was to knock down miles to get from point A to point B. It would have been much more fun to do what you propose. To my traveling party's consternation even then, I'd whip it off on a random exit to see the worlds largest ball of string or whatever and I highly recommend you not schedule yourself too tightly.

And, those Cayans are sick quick. I loved the one I drove. But the woman opted for the egg's older brother I posted a picture of a while back.

Edit: I saw Porsche and Cayman above and thought you were talking about a Porsche Cayenne, which we test-drove. Then I proceeded to misspell it. FML... I am intoxicated.