You do not say if your SUV is a true 4x4 (low range) eg a Fortuner, is an "all wheel drive" / "four motion" SUV like a Subaru or VW Tiguan and if it has a manual or an automatic gearbox and if it is a diesel. All these may change one's approach.

Going down a steep hill is not a 4x4 speciality. Even a normal sedan can go down a similar hill providing the surface is sound. One needs lower gear ratios to climb, but brakes to descend. Ask any true 4x4 driver with an automatic gearbox. Automatic gearboxes do not utilise engine compression for braking in the same way manual gearboxes do.

I think there will be no difference, as the speed reversing a trailer down will be so slow that the only traction will be from the brakes.

Going back up I would opt for the 4X4.

Hurricane, you say "Most of the newer SUV's and even 4x4 bakkies like the Ranger have difflock and hill descent control making the auto box argument a non-event." What is your guess, what percentage of of 4x4 bakkies on our roads have automatic gearboxes and hill descent?

My understanding of hill descent is that the brakes controls the speed with which you descent automatically. I can recall when the Land Rover Discoveries first came out with traction control they did not have any diff locks, and the motoring writers expressed their concern about the life expectancy of the brake pads.

HM, my experience is that a vehicle's braking ability when going backwards is far less than when going forward. I think it has to do with the design of the system, expecting perhaps as much as 80% of braking to be handled by the front brakes. In reversing down a steep gradient this could very well result in the front brakes locking, whilst the less competent rear brakes are left to control the descending speed.

Unfortunately Des's question gives too little information to give a meaningful answer. Perhaps once he has given us the specifications of the vehicle involved one may consider an appropriate response.

Kanneman, I think we are in agreement that the only traction will be from the brakes while reversing a 1.5 ton trailer downhill, irrespective if it is 4X4 or diff lock. Engine compression etc will not come into play at that speed. 

In my opinion the only other factor to be considered is the weight difference and tyres of the vehicles.

HM, if it is a diesel bakkie and it is in low range in reverse the engine compression will aid those rear brakes tremendously in controlling the pace.

The only time the engine compression in low range will assist is when the brakes fail. Dan moet jy jou reverse met 'n 1.5 ton sleepwa ken boeta.