Out of those models, The Cayenne Turbo is much more attractive as it's a fairly exclusive model, they don't make many at all. Plus, as indicated, despite the weight, very powerful and capable vehicle.
Unless the X5 get the v10 m5 engine...maybe call it the MX5 (hehe, BMW miata)...its not really comptetive with a cayenne turbo.
MB hasn't really had a factory SUV (AMG or otherwise), that can perform at the sports car levels. Obviously the big MB tuners can make anything happen, but their prices even exceed what a stock Cayenne Turbo would cost.
And back to my Subaru post, for approx $120k, I think a Forester XT, with a seq shift rally trans, modified turbo engine, a complete body teardown w/structural enhancement, upgraded sus and brakes, you could get a reasonably serviceable SUV that would go further off-road, carry as much stuff and be faster than any of the above.