Thanks to everybody for the input so far. After researching on tire rack I see that the load rating of the Michelin Latitudes is XL, higher than others.

since I tow two different 5,000 lb boat/trailer combos at highway speeds I think the Latitudes would be the best compromise for me.

any further thoughts from those of you who tow things with your X5's? (mine, again is an '04 4.4 with sport package)