I think the considerable wieght saving would make all the difference .
I haven't used the yam but hired a boat of similar size to mine with a new honda 90 vtec while on holiday , the etec i have has lots more go than the honda and although i have done a direct comparison uses less fuel for a similar day out .
I also tried the demmo of my boat with a 75 etec and that had a lot more go than the 70 suzuki 4 stroke i was used to on a much smaller boat.
I did worry about trawling with the etec but it seems very happy to trawl when fishing at low revs and there is neve a hint of smoke or oil fouling when I open it up again .
i always felt confident with a 4 stroke when trawling but my worry with 4 stroke is that the oil pressure is quite low when ticking over under load which can't be doing the motor much good iether ,
My intention is to use my small aux motor for fishing when i get it rigged , and the cost difference there would buy you a small aux