Fuel for 1990 150hp Mariner Magnum II?

Hey all, I am new to the forums.

We have had our bass boat for almost 15 years. In that time, our oil injection system failed, and so we brought it to our local marine mechanic and he took that system out and fixed our motor so we mix our gas now.

We have been using Supreme (91 Octane) gas ever since we got it, but now I am hearing a lot about how the more expensive gas does not give you better performance or fuel economy, it is more to prevent knocking, so it all depends on what the manufacturer recommends. Is it time to start buying Regular (87 Octane)?

I am wondering what fuel Mercury/Mariner recommends for my 1990 150hp Mariner Magnum II, and also checking that I should be mixing my gas 50:1?

Thanks

My Owners Manual specifies a "minimum" 87 octane fuel to meet the published specs. Well, if you are a high jumper, do you travel over the bar with the hairs on your legs touching the bar or do you give your self some error room? What about the volatile components of gasoline evaporating over time and that effect on usable octane? What about the components making up the "recipe" for premium fuel and their impact on performance?

A couple of years ago I switched to 91 and noticed a significant difference in starting ability, idling ability, and hole shot performance. The argument is unsolvable since users have their varied opinions for varied reasons...just like my comments above......it really boils down to what gives your tummy a warm feeling when you tuck yourself into bed every night! I do find that Pennzoil Premium Plus 2 stroke TC-W3 oil provides premium, almost smokeless performance in my engines.

On premixing, I changed my 2002 90 hp after 10 years of operation (POs and mine) for that warm tummy feeling....no other reason. Several years later I didn't change a 2002 115. Tummy still warm. Go figure???????