c-30 Cat Engines

I've always liked the 3412. I understand the C-30 is a real close cousin but can not tell you what those differences are. You should not be disappointed unless the dealer or installer messes up.
My next personal thought is; Stay away from MTU.

To big? Loud?
I remember an article about buying a boat with future sales in mind; At that time, the thought was buy the larger hp package and your resale would be nicer.
I have always felt a boat with larger hp ratings would out last a lower h p rated boat. Fuel has been a sore subject for many years now, I just can not see anybody abusing the slightly larger h p boats. Dolors per mile will keep even the most insane operator (owner) from wot. On the other hand, lower h p boats have to be run harder to keep up, look good, or keep on step when fully loaded.
Properly maintained C-32s may be a better venture if you also keep your foot out of them.

I have not heard of (here in south Georgia) any C-30/32 repeated issues. Any MTU is an automatic issue.
South Florida has all the MTUs and MTU (big bill) mechanics and headaches.

You may be dealing with more boat & exhaust design than the engine making all the noise.
Please run a C-32 in another ship (or more) before considering the loud operations an issue (between c-30 & 32).

I'm death in one ear and can not hear in the other. But still, It's hard for me to tell the differences except near wot.

yep...

Cool, I did not know there was a major difference. I hope the problems were corrected? Still better than a MTU?
A question that came up was noise, Would you think the installation would contribute to higher sound levels or could the C32 be a real noisy beast?

The biggest trade off to bigger engines is loosing ER space not fuel... As others mentioned if you can restrain yourself you re not going to burn more and the biggest benefit is that the engines will last much longer than the smaller ones as they won't work as hard

For instance in the 70' Johnson I run, the 1400hp 2002 vintage 3412Es burn 80 to 85 Gph combined at 22kts but that's only a 60% load. I don't even know what speed / burn we d get at 80% as i never run there, probably 110 Gph for 25kts...

But at 60% they will last a lot longer than the base 1100hp engines that will be run at 80% most of the time, more than making up the additional initial cost

The down side is that any ER work feels like a 2 hour yoga session

I like the MANs. Your decision to go with MANs should be carefully researched. You need a real MAN local shop (or two) for support.
There just is not many out there and not all are good.

Visit both a MAN and CAT dealer and get quotes for routine services for the engines you are considering and compare costs over 2000 hours Also compare part prices for common things that will need replacemnet over that time like impellers, starter, filters etc

Here are a few numbers for 1400hp 3412Es
Level 3 service (3000hrs) $5000 incl valve adjust and aftercooler removal/clean
Level 1 service (1000hrs) same

Impeller $250 (lasted 4 years / 2000hrs) and still good when removed. Takes an hour or less
Starter $500, easy swap
Fuel cooler $1000. Also under an hour job

I just did an oil change (incl fuel filters) for about $850 in parts, took me 6 hours. The bulk of costs being 45 gallons of oil incl the 2 gensets

I wish I could list more costs but the above have been the extend of costs in the last 5 years

On one boat, we went for just a stb control board for run-away hour recording. "Known problem". The same f%^&*ng day the stb board was replaced, the port board was showing 25000 hours and climbing.
What was that Star Trek quote; hours are minutes?
The sensors are expensive and are the cause of a lot of false errors and problems. I have heard stories, but the blocks I service (4 crm 900s & 2, old V-10 1000's) are solid (knock on something good).
Just wish there was a good area shop.