My chipped 4.4i X5 returned 23.8 mpg on a brisk run recently and a friends 3.0d X5 with a sprint-booster showed an average consumption of 22.9 after a long run so I would say about the same.
Good grief that 3.0d must be poorly! We got 32-34mpg on a longish (300+) mile run to France this Summer in the X5 3.0d. Just set the cruise to 90 (so real speed on GPS about 83-85). We always get over 30mpg once out of town. In town, 25 is the norm for us.