Your TQ numbers far exceed Cobb's claims for that map (43% over stock). You're in "better than N63," territory. If for a fact you could achieve 500 ftlbs in a 3.0L engine, that is not a diesel, I'd do it tomorrow. Why by an X5 with a V8 at all?
Something is a miss in the numbers, that are easily to blame on the dyno, or dyno operator. The easiest is gear ratio. There is a way to skew things with the temp probe, or even correction factors.
here is a good example, the 2nd one is my favorite.
(the sound effects are awesome here)