I used to be partial to carbed engines - no chance of clogged injectors, etc. although you still need to use Stabil or equivalent to avoid fuel breakdown. Now that I have a DFI motor however, I realize that it's sealed fuel system (except for fuel tank) prevents a lot of fuel oxidation, etc. Also had a clogged jet on my old '75 115, which can be fatal on a premix 2S due to oil starvation. Fortunately I caught it during a WOT sea trial I did while preparing for a Bahamas trip, but it was subtle - just minor surging after about 20 sec @ WOT. I might not have caught it had I been running a bigger motor!
I also like the 115 E-TEC and might have bought one instead of the 150 if they had been in production at the time. Ethanol is a whole 'nother issue - BRP says the E-TEC's can run 10% ethanol, but I think the danger is that if you get much H2O in fuel tank, the ethanol will combine with the water and separate out of the gas, so you'll lose a bunch of octane and risk destruction from detonation. As for motor SIZE, if you consider that the 20' hull was designed in mid 60's for the "big" 275-300 lb outboards available at the time, then you realize that using of a much heavier motor will tend to screw up the balance and self-bailing ability of the boat.