Your reason (towing) is the only reason I would move to an E53 from an E46. I pull my E36 M3 and trailer with my X5 and it does great! The Steptronic works surprisingly well when towing. Ours has 122k on it without any major problems so far and the previous owner also used it to tow his trailer and car. I have a feeling that I'm driving the car on borrowed time until something major goes wrong but I feel I got a good enough deal on it to justify the potential repair costs.