My sailing club has a Raider 4.8 (Same as the Ribcraft 4.8) with a 50HP Mariner 4stroke (not efi), tops out at about 30knots and feels like it needs more power, ideal for a rescue boat though.
Ribcraft have fitted several with 75HP ETECS for skiing although I think they have been sold to employees.
I had a friend with a 4.8 powered by a 60HP Mariner EFI 4stroke, very nice combination, did around 35 knots and extra economical. I have found the EFI 4strokes to be more responsive than the older designs still running carbs such as the Hondas. A 60HP 2 stroke would be lively, how about a Tohatsu 50 TLDI (direct injection, do they do a 60HP variant of this????)