I agree the opti is noisey.... The opti on the back of our Redbay is noiser that the 2x75 fichts that We had before ... But I like the noise ...
I dont think the Suzuki or Etec will be much better on fuel, than the opti , and you have to change everything , from control cables to wireling loom etc etc ... its a really big job
..... If I was going for a new boat I would probably go for the Etec , as 4strokes are more hassle then they are worth , with extra servicing and more moving parts to to look after, and the extra weight exactly where you dont need it.