mabrodb,
In terms of fuel consumption in a typical UK environment max cruising at 25,000ft with the propellers at 850 rpm and the power levers in the rating detent total fuel flow is approximately 1100 kilos per hour.... yes I did say total i.e. both engines!!!
This figure is a typical summer fuel flow with temperatures being around ISA+10 at cruising altitude of 24,000/25,000ft. This would also mean that you are cruising just below VMO (red barbers pole). Thus indicated airspeed of around 250kts.
If however you were to bring the power levers back to maintain Indicated airspeed of 210kts in the cruise, then your TOTAL flow fuel can be improved significantly to approximately 730 kilos per hour!
The latter procedure is a great way to save fuel especially if your running early. It helps if the duration of the flight is greater than 1 hour so you can clearly see the benefit from this technique.
Mind you with such a good fuel burn already you may be more than happy with 1100kgs, but its great tool to have the ability to reduce that further. Of course this is relative, however if your planning to have a large fleet this can significantly reduce your fuel bill!
Please be advised that if the aircraft has drop down masks in the cabin then the max cruising altitude with be 28,000ft but I don't have figures for that level, perhaps someone else can help here.
Aka