While I agree 100% re: fuel cost for the old detroit diesels, your comments about better fuel economy in the hatts over the viking have me baffled. The 43 hatt or the 44 Viking would have the same DD's in them, similar displacement, etc. and in my experience, fuel economy, or the lack thereof!!) would be nearly the same between the 44 Viking and a 43 hatt.
But as others stated, unless you want a REALLY loud boat that drinks fuel like crazy, you would not be happy with that boat. Personally, I don't like loud engines and DD's are about as loud as they can possibly get. It also gets old if you go for a cruise for a few days- hearing the noise of those DD's for 8 hours a day can wear you out unless you really like loud engines in which case you would love the DD's.