I had three years with a D120 (no airbrakes). Cruise was happily in a range from 75-100 with rpm appropriate for the C90 and a fuel burn of 15-18lph. I tended to cruise on the slow side, to enable loose formation work. They do what they do, most efficiently. I can't remember the ROC, but better than 500 fpm and the short field capability was impressive, especially during wet winter conditions.
Given the small queue waiting to buy her, I think I had a good 'un, on the lightweight side. The current owner might be able to help with figures if you want me to put you in touch.