IBG
There are two ways to cool your engine. One is with excess air/oxygen and the other is with excess avgas. Excess air works quicker,is cheaper plus your plugs and combustion chambers look like new at every 100hrly. 4,000 + hours on a IO520M C210 operating this way have convinced me. Cruise 2,400 rpm up to 8,000 ft then 2,500 rpm above that.(You don't fly a 210 to go slow) Manifold pressure not above 24 inches down low then whatever you can get up high.
GG
Re turbines. When the initial cost,the specific fuel consumption and the overhaul/maintenance costs come within a bulls roar of our nasty reciprocating engines let me know.
Cheers RA