You guys need to think outside the box...wait, no. THE box. I present to you my best guess, the W463 Mercedes-Benz G-Class (1990-Current). Available as a 250GD with an astonishing 94HP, or as a 621HP G65 AMG. That is a 527HP gap for the same vehicle.

I would like to retract my statement about a C5 Audi A6, I am sticking with a B5 Passat. For now.

It doesn't look like an E39 to me. Too rounded. My first guess is a B5 Passat or a C5 A6. Window lines are wrong for an A8.