[Fr. Frank]

I am pretty sure I saw an article on one of those gofast boats, or an SKA hull, where they compared, as closely as possible, three different outboard options (like triple verado 250s, twin yami 350s, triple etec) versus diesel i/o with jackshaft. From what I recall, the diesel I/O was not that far off on top speed. Like maybe less than 10%? Where as MPG as cruise was like 2x or 3x... price was about the same.

Yes. The '04 26' Albin with the 5.7L 270hp gas VP sterndrive with the motor under the console and jackshafted to the sterndrive (VDH hull) was the least expensive purchase option, new, for that boat. Projected life: 2400 hrs.
The twin 200 hp Yamaha HPDI's outboards were the fastest, but $9K more than the gas sterndrive. Projected life: 2000 hours.
an extra $16K over the gas sterndrive, you could get the 250 hp diesel sterndrive/duoprop. Projected life: 10,000 hours.
This diesel option got you 12 mph less than the outboards, and 7 mph less than the gas sterndrive at WOT. Recommended cruising speeds were 7 kts less and 4 kts less, respectively.
Volvo claimed it used only 7.4 gph at 21 kts cruise, compared to 13 gph for the gas sterndrive at 25kts, and 25 gph for the twin outboards at 28 kts cruise.
That's a fuel cost per operating hour of $29.60 for the diesel (at current marina price of $3.99 per gallon), $53.56 per hour for the gas sterndrive (at $4.18 per gallon current marina price), and $104.50 per hour for the outboards.