How much power/torque does a tow car really need?

I had thought I was quite happy with my 140 bhp Mondeo diesel pulling our 1350kg (MLTPM) van.  That was until I was driving out of Bath on the A46 yesterday.

For those that don't know it, it's a very steep hill that seems to go on for miles, with a 50mph limit and a crawler lane, plus a sand trap on the downhill in case your brakes fail!

I did manage to get to 50mph, but the poor old Ford was working it's socks off.  If I'd had to slow down for a junction or slower traffic, it could have been a real pain to get moving again..

So the question is, just what kind of power to weight ratio do you need to comfortably pull a van in all conditions?

Forgetting about BHP and the old recommendations, which seems old hat in this diesel dominated era, my car has 320 Nm of torque.  That works out as about 240-250 Nm per ton, depending on loading with my van.

I'm starting to think that might be the absolute minimum if you want to avoid long uphill climbs at 20mph with endless queues behind you whilst you rev the nuts off your engine and the turbo turns a funny shade of red.

No doubt, many here have made do with less.  What do you think?