Steve, I would look at those Honda tests with a bit of skepticism. The "Tests" always get much better mileage than real life conditions. The boats are new, are very lightly loaded. Generally the "mileage" is in the 2.2 to 2.5 miles a gallon--more at displacement speeds.
Since the injected 90's are new engines (boat show this last year I believe)--it would suggest that these are not the origional engines on your boat.
I don't know if twin 90's will get better mileage than a single 135 or 150 Honda, which is the "usual" engine on these boats. There are lots of variables.
I strongly suggest that you put in fuel flow management systems. You might consider the Honda, or put in the Lowrance with either 2" or 4" read out, or Navman/Northstar. I have used both of the latter and they work quite well, cost will be in the couple of hundred of dollars, and in the long run they will save you that much in fuel costs. You will find out instantly what trim, different speed, motor angle, etc will do to the fuel consumption and find the most economical speeds. It is a real eye opener that a few degrees of motor trim or trim tabs may make over 10% difference in the fuel consumption.
Welcome aboard and enjoy a great boat!