Towing: 35i vs 35d

[dnadrifter]

So I am fortunate enough to have two E70 X5s: One is a 2013 35i and one is a 2011 35d. We ordered the 2013 new and will likely keep it a long, long time as it has all the options we wanted (including AD) and is in great condition since we have had it since new (my wife is the primary driver). I liked it so much I searched for a 35d and purchased a CPO at a decent price in the color combo I wanted.

So....I am planning on having an invisihitch installed that I am planning on towing about a 4500-5000 lb boat behind. I assume the 35d will be better at pulling the boat, but I also know I will likely have the 35i for much longer. I don't really feel like putting a hitch on the 35d, but then having to go to the hassle of taking the hitch off and getting it installed on the 35i (with all of the harness wiring, coding, etc) after a few years.

So, how much better would the 35d be at towing a 5000 lb boat. Any opinions? Any first hand experience with both?