We tow a 2004 Swift Challenger 550 with a 2003 Volvo V70 T5 Auto.
Obviously with 250 BHP on tap you don't get overtaken on hills but you do pay a heavy penalty on fuel consumption as its a 2.3 turbo charged petrol engine. The traction control gets a good workout when pulling out of junctions!. The auto (Geartronic) box copes well with towing.
I know several people with the D5 V70 and they report excellent performance and MPG (wish I had gone that route in hindsight!).
The Volvo is like driving an armchair and the build quality is faultless. I have covered 55,000 miles in 2.5 years without problems. I drive it fairly hard when solo and don't look after it at all (company car if you hadn't guessed!!!). Most of HM's Police Forces use them so they must be pretty good.
The climate control is excellent too.
My only real complaint is the steering lock which is hopeless - it won't go 360 degrees round most mini roundabouts in one go!!!.
Still, it's a TD5 Discovery next - far better in the mud!!
David