I've always thought it would be nice to have diesels, but with my 8.1's 3600RPM achieves 30MPH and 4500 WOT hits 38.5 MPH. Cruise speed nets about .8 mpg. I would expect the diesels to produce higher cruise speeds and lower fuel consumption. Until you talk to another 340 Diesel owner you won't know. There was a member here from Ohio that had one, he ended up moving to a larger vessel (non Sea Ray if memory serves) but think he's still on CSR. Hopefully he sees this post!