Yes CRAN I absolutely agree with you that those performance figures seem to be overly optimistic to me as a layman.
However we do not know yet if the SMA 230 is overworked when producing 230 hp constant!
Usually aircraft engines are not designed like car engines, where the car/automobile engine is only designed to produce its rated horsepower for less than 25% of the time and aircraft gasoline engines for less than 75% continious power.
Lets hope the SMA and other diesel engines were designed to produce rated power 100% of their operating time, does any one know?