My 23' is powered by a Volvo D3-200, and will cruise 28 mph @ 34-3500 [at 7 US gallons an hour], and top out at 36 @ 4000, burning 10-12. Island Outfitters had a 26' Hourston with 225 outboard that would go over 40 mph [no flybridge, Robert].
I think there's a lot of focus on bigger motors because they exist now, not because you need them to drive the boat at reasonable speeds.