as a former owner of a C30 (1981), I say get the bigger engine. Mine had the 11 hp, and it was fine for motoring around the marina. I got into some trouble motoring into a wind of about 25 knots. I ended up going zero mph into a pretty rough sea at full throttle. Very scary situation. My latest boat has the bigger motor. I would make that a priority. One other thing, when I sold my boat, several brokers wouldn't even consider listing it because of the small motor. Wierd, I know.
Good luck, Bill
Odyssey, '79 CSY 44 Cutter
Channel Islands, CA
"There is no unhappiness like the misery of sighting land (and work) again after a cheerful, careless voyage."