Having had Northstars and having flown a couple of Arrows all I can say is most of the Arrows have ended up in the dumpster and we still have Northstars that are 10 - 15 years old. My advice; forget the fourstroke and put in a honking 46 - 55 and live with it. These are both fast airplanes and don't take to put-
putting around the sky. If you want four stroke power look towards a laker or a more conventional layout.
Can't say I agree with tip floats on the Arrow; they are very sensitive on the water and any tip drag will induce a spin out. Both planes need to get up to speed and on the step and then allowed to fly off. Once in the air the worlds your oyster.
Peter