Time to resurrect my own old thread. I recently returned from a whirlwind 4-day round trip to Arkansas to fetch my daughter's stuff. Packed the biggest dual axle UHaul trailer to the gunwales and lived to tell the tale. We towed a round trip of 4500 km and averaged 8.6 l/100 km at a fairly steady 120km/h on the way down sans trailer. Average l/100 km for the return trip hovered at around 13.3 though my calculations show a combined trip average of 11.3 l/100km. Empty weight for the trailer is 1920 lb according to UHAUL -->
https://www.uhaul.com/Trailers/6x12-Cargo-Trailer-Rental/RV/ The thing was stuffed with my daughter's kaboodle, so I'm going to estimate 4000 lb laden.
Verdict: The Q5 pulled like a champ. The trailer was almost as heavy as the tow rig but there were no issues, probably because of the built-in hydraulic surge brake on the trailer. Once I had it adjusted, the Q5 didn't feel it. While the car does hold the gear longer when accelerating, it does so smoothly. Braking wasn't an issue either. Likely the Q7 will be just as good.