Have not been on a sailfish I/O. Typically most I/O Grady's were much slowe rthen the outboard counterparts, but most did benefit from better fuel economy. The down side to an I/O is the loss of cockpit space and having to work around an engine box, to some it is not a problem, to others it is a huge pain. Personally I hate anything across the transom...engine boxes, seats, euro transoms with livewells and fish boxes. I want a clean transom with nothing or just a center mounted kill box or livewell that does not extend more then the middle of the cockpit. As far as ride, I have been on a few I/O Grady's and they all ran with a more level trim then their comparable outboard models, good for efficiency, but not always for ride. Moving weight forward in the boat though, does improve ride, so trim might not be ideal, but weight location is improved, so in certain conditions the I/O version will ride better and in others worse. I/O versions typically have more vibration due to the engine mounting and location, to some not a problem to others they hate it. an I/O is a great engine to work on for those who are handy, they are similar to car engines, if your not going to do much work yourself there is no benefit IMHO. I personally would not want to have to worry about a boot and joint all the time, I see guys in my marina always replacing them or having problems, but some guys love them and get tons of use out of them. They are not for me but some like them. As far as a single on a sailfish, going to be a pain to dock and manuveur in tight quarters, you will not have a ton of control, ideally anything this size should have twins when feasible.
The big question is are you ok with an I/O, some love them others hate them and would not go near them. If your comfortable with an I/O, the boat should not be a bad one, but would still require a sea trial. If you are more used to outboards, chances are you will not care for the I/O setup. Personally the only I/O setup I've ever considered was a jackshaft setup where the engine is more forward where weight is ideal for ride, and where it eliminates an engine box at the transom, although I personally will not buy an I/O, either outboards or straight inboards for me, or possibly ips/zeus down the road.
