Bear in mind that this is coming from a bloke with a twin engine boat (for sale) & who has a single engine boat on order:-
Twin engine, I specced this as a dive boat, the rationale being that we were diving 20+ miles off shore, deep stuff. If I put divers in the water, I wanted to be sure that I could get them out again, especially if they've been drifting a couple of hours doing deco. The boat has completely separate fuel & electrical systems for each engine, it will plane on one engine, the fuel tanks can be combined to a) run both engines from 1 tank, or b) 1 engine from both tanks. This means that the loss of 1 engine or 1 fuel tank doesn't mean you lose the corresponding engine/fuel. Similarly, the batteries can be combined to run/start/charge from any engine.
I've even gone as far as having separate plotters/gps so that failure of one unit doesn't mean the loss of the whole system, paranoid moi???
New boat:- Single engine, smaller boat. I've stopped diving & now don't need anywhere the level of redundancy. We still do the distances, but usually in company. We are well equipped with drysuits/plb/290N lifejackets yada yada! If it all goes brown, the worst that happens is we drift/anchor & wait for the cavalry.
Twins are undoubtedly more expensive to buy/own/keep. In your case twin 40s will nowhere perform as well as a single 75 of similar pedigree. Unless you have under deck tanks, you will have fuel cans all over the place gobbling up valuable deck space.
At the end of the day, it's your call. You did ask