I borrowed a mates tandem tip trailer for a tip run a while ago. The Defender (300 Tdi) towed it effortlessly up-hill (80kph speed limit).

When I got to the tip, I was surprised I weighed in at 4,500kg (vehicle & trailer). Accelerating & braking and overall control felt much better than it would have with the 3.5 RRC.

As far as economy goes, I have a small off road trailer and I delivered a couple of fridges (standing up-right on a trailer bed that's waist height) to a friend 200km away (100kph highway run) and I used about 1.2 litres per 100km extra with the drag.