I have thought about an electric trolling motor just to get in and out of the slip. It seems like that might be a viable option for someone who mainly daysails.
On the original topic, my 6hp yamaha 2 stoke and the old suzuki 8 2 stroke moved my boat just fine. The 9.9 2 stroke on Ariel Spirit was too heavy, and made too much thrust at anything more then half throttle. The merc 9.9 was hard to drop in the well, and is even harder to remove.
IMHO, a 5,6 or 8 hp is pleanty, and the lighter the better.
FWIW.
On edit:
I just did a search, there are pages and pages of threads on outboards. Each time we start a new one, it makes the next guy have a harder time find their answer (having to seach through multiple threads). It might help if we could merge some of them, and all remember to search the old threads before starting new ones.