You're expanding your original statements:
The P2006T has demonstrated 100 fpm climb on one engine @ 7000 ft @ MTOW (single-engine ceiling) to the FAA. With 880 lbs of payload and a power output (according to Rotax) of 75HP and the high-altitude performance penalty, IŽd say you can easily do that on even less than 75 hp. Not to mention the Twin-R which is 750 (!) lbs lighter, aerodynamically cleaner and uses the exact same engines.
Climb performance by the way is formulated in climb gradient, for various scenarioŽs. Page 1-B-7 and further:
http://www.easa.eu.int/agency-measures/docs/certification-specifications/CS-23/CS-23 Amendment 2 (corrigendum).pdf
(Far-23 is virtually identical)