It does make a difference, but I was exaggerating and exercising sarcasm.

I ran a 90 Opti on my 20' Seafari for 5 years and was happy with the performance. I had no need for exceeding 30 kts because in anything over 2' seas I occasionally got airborne with the previous Merc V6. Yes I could touch 46 knots/53 mph knots in a very light chop, but just over 1 mpg in a 20' family fishing boat is silly.

But it is true that when you mount 450 lbs for a motor you really need a stern-lifting prop.