I owned a 2005 Yukon XL with the 8.1 and loved it. I sold it becasue I had a itch for the newer body style 2500 with the 6.0 and have since sold it to find another OBS with the big block! If you can find one with the 8.1 get it over the 6.0. My experience with the big block is that mileage is basically the same and actually a little better towing the boat than the 6.0. If you are doing any towing at all, do not buy a 1500 Suburban with the 5.3 as it is not enjoyable at all to tow with. They are designed as soccer mom vehicles. If you want a tow truck, you need the 2500!
1955 Century Coronado
1968 Century Cheetah