I do not have any experience on the higher output C 18's but can say I am very happy with the 3 X 435 ekW Gensets I have been using on a recent project. I encouraged the Owner to upgrade from 3408'S and am happy with the result.
These are the single turbo ones running at 1500 RPM.
There have been a couple of sensor failures and some leaks not all of which could be blamed on CAT. They do not burn any large amounts of oil and always run very clean.
I seem to recall reading about the first pair of the high output C 18's that were in service, they were used on a game boat from somewhere around Beaufort, NC/ Cape Hatteras area.
The boat operator gave them a rave review, I can't remember if it was a new boat or a re power though.