The Problem With Small Turbines
"...small aircraft are penalized by the pitiless exponential mathmatics of scaling down..."
Air & Space, p. 22, Oct/Nov 2005.
The problem with small turbines is, they are small.
To get any kind of efficiency, tolerences must be tighter, rotor RPM's higher, hot section temperatures higher, accessory gear boxes don't scale down. Small turbines lack the capacity to produce adequate bleed air for pressurization, nacelle and wing anti-ice.
Again, compare the Cessna Mustang to the Eclipse. Both have nearly the same cabin volume, both are intended to fly at the same altitudes with the same pressure differential. The Mustang engine will have 1,350 lbs of thrust, the Eclipse 900 lbs.
When you start extracting bleed air for pressurization, the Eclipse will pay a proportional greater penalty. This will show up if the engine lacks the power to get to altitude with a pressurized cabin.