[6] The Beechcraft 60 was, despite its very good performance, only a moderate seller, principally because the complicated technology demanded a high expenditure on maintenance.

Normally, pilots figure 45 gallons per hour (170 L/h), plus another 40 US gal (150 L) for each takeoff and climb as typical fuel consumption for cross-country planning.

Called the Royal Turbine Duke conversion,[8] the modification increases fuel capacity by 28 US gal (110 L) and the maximum useful load by 400 lb (180 kg).

In reviewing the aircraft in 2008, Rick Durden of AVweb stated,[12] Built to the quality standards of a King Air, the six-place Duke sported 380 hp [280 kW], Lycoming TIO-541 engines – rare beasts, those – which means when both come due for overhaul, the choice is the overhaul or buying a small house in the Midwest.

The assertive lines of the airframe made for a startlingly attractive airplane, but led to high costs of manufacture and, surprising to the casual onlooker, horrendous drag.

There are those who claim that the Duke was purposefully designed to be about 30 knots [55 km/h] slower than it could easily have been on the available power simply because otherwise it would have been faster than the flagship of the Beech line, the King Air.

The roughly 230-knot [430 km/h] maximum cruise speed is only marginally less than that of a King Air 90 and about the same as a Cessna 421, which carries more on slightly less horsepower.

While the Duke shares the delightful handling of the Beech line, should pilots have the joy of single-engine operation, they will be up against the highest rudder-force of any piston twin – 150 pounds-force [670 newtons] at Vmc – which happens to be the maximum the FAA allows.