Twin Etec 115's for a 23'?

[Fr. Frank]

I was reading on another list and saw where a guy with an 1985 23' Chris Craft Scorpion WA is running twin '05 115 Etecs, and claims 3.3 mpg at 24 mph & 3800 rpms with 19" pitch props. He said he has to change the prop to get up on plane with one motor, though, changing from a 19" to a 15". Nothing on what kind of props, though, or on what his WOT speed is.
I put the data above plus the 115 Etec gear ratio and calculated slip into a prop calculator and came up with 39 mph at 6000 rpms.

This morning in Destin I saw a early 20' Seacraft SF with the wide transom cutout rigged with twin brand new 60hp Mercury 4-strokes. The boat looked good. It was in front of me trailering west on US 98, and had a Mississippi plate on the trailer.