How about a series of holes in the rear window, assuming it's polycarbonate (can't remember through the alcoholic haze )
Is the window being sucked out (unlikely you're going that fast) or blown out (pressure build up). If the latter it'll be a parachute effect that you could well do without so the holes will relieve the pressure.
I'll edit in the morning :roll:
Handle every stressful situation like a dog. If you can't eat it or hump it, piss on it and walk away!