I would not expect the gains to be the total of the individual claims either, though my experience with Dinan is they are conservative about gains. My experience with BMW is that the ratings are close enough to fall within dyno to dyno and conditions variations.

Over simplified, torque gets you going and horsepower keeps you going. Since the X5 weighs so much, for street driving, where there is a lot of acceleration from a standing start, TQ increases are the key numbers. There will also be HP gains but they are not as beneficial on the street as torque will be.

If I use only Dinan Mod figures they posted for the 4.6 the stock horsepower was 340 with TQ at 364. With the Dinan mods of their exhaust, throttle body, engine, software, air box, High flow MAF the HP was rated at 369 and TQ at 382. TQ and HP peaks were calculated at the same RPMs as stock peaks. TQ gains would be noticed at about 3500 RPMs. HP benefits wouldn't be much help until about 4,500 RPMs. As you would expect the TQ and HP gains continue to improve as RPM reaches 6,500 redline. What all that boils down to is that a stock 4.6 should stay with 4.6 with Dinan mods until about 3,500 RPMs. From there on through the gears the Dinan modded 4.6 should slowly walk away. This would somewhat similar to two 4.8s though without the engine software matched to the other mods the difference would most likely be less.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas