Do not know of an MTI with only 485hp that ran over 100, that would pretty tough to do, it would have to put nearly every drop of Hp to the water - if they did that's great!
6LPA's - not enough Hp to do much, not being mean a great very fast crusing boat Im sure but not high performance. Remember I ran a 34' with 300hp Cummins B's and i loved that boat, 50-55 all day and night but you know just can't run with the big dogs! That's why you need that 500hp -575hp just like a Merc to get head turning speeds.
As far as drives go, I say it 1,000 times on here the torque means nothing, you need Hp & RPM to go fast. Every fast boat on here, just read when people yap about being out of prop all the experts say "get taller gears" next. You could put #6,#7,#8, #9 or #10 drives (I'm guessing Merc will get there some day?) on the boat and it won't go fast without prop speed.
I love Arneson drives but they are not mainstream they are fringe - no offense RIK you know I think they are the best!
the equation is simple:
diesel + OD box + Bravo = Speed
When you use a reduction on your gas engines in the drive you multiple the torque - right?
Math is math you raise the RPM on the diesel keep Hp constant and enter the drive at the same RPM as the gas engine would and drive sees exactly the same stress whether it is gas or diesel - ask Fred K, we have had that talk over Gin & Tonics many years ago several times before his drive was a Merc drive.
Digress here for a moment about duramax, they have another problem that most V-8's have, the exhaust should be on the inside of the V and not the outside - why? The hot exhaust gas takes a larger area than the cooler intake air plus the water jacketing makes the engine wider. When the exhust enter into the V you have 1 casting with water jackets going into a central turbo charger with the intercooler mounted directly in front of it and then intake pipes to 2 narrow manifolds along the outside of the block. The profile is narrow, the hot areas are contained in a smaller space overall you get much closer the demenisons of a gas engine.
Again you will not ever see diesel perfomance engines make a strong hold until you can drop them in place of a Merc on a Mrec drive and have equal speeds.
Yanmar & Cummins broke into the market that way, by repowering Bertram, Blackfins and like that had gas engines or heavy Cat 3208's in them. They proved themself and when older repowered boats were passing newer boats then the OEM started installing those engines fromn the factory - you can not beat a proven & successful way to market marine engines. You need to the same with older Cigarettes, Fountains & Nortechs and people will notice.