It's actually pretty crappy, that's fixed gear -300 speeds on similar gas. The real reason for the differential has to do with the cylinder compression ratio differences between the turbo and NA 540 engines, plus the bonehead move of using fuel to cool the engine. The NA Lance does 145-150KTAS on 14GPH by comparison, a power setting that can be sustained to 10Kish density altitudes at even sedate (2400RPM) prop settings. Similar dynamics exist with the Turbo Arrow and NA Arrow. Basically, turbo boosted (not to be confused with normalized) cylinders are much less efficient than the NA variants. This is overcome in the turbos by going high enough to compensate for the poor fuel usage. In the aggregate a Turbo Lance is faster than a NA Lance. But it's not faster on a per gallon basis at altitudes where the NA engine can attain the selected power setting. This is compatible with what @Unit74 is witnessing with his Turbo Lance. I still think his is on the slower side of things for a Turbo Lance, compression ratio issues notwithstanding.