I have owned the first generation and the new gen X5 V8. I never towed with either, but they are great cars to own. Other than abysmal gas mileage, they both have been trouble free and very nice to drive. If you can swing the extra cash, the new version is a nice upgrade in terms of space and packaging. I have no complaints about either. If lack of availability of stations that have it in my area was not an issue, I would have gone with the diesel. I would think that would make a terrific tow vehicle and it gets 30mpg (unladen) on the highway.
Sorry I cannot help with towing info.