X5 and Q7 can do 3500 alright.
Not sure if the X5 can do 3.5T, nor would I want to tow that weight with any BMW!
Land cruisers, defender, discovery, range rovers, Q7 or touareg are the ticket if you wanted to tow heavy kit regularly. Few of the pickups are rated for 3.5T and they're generally pish for towing with as well.
Low miler Disco 3/4 or land cruiser