John, sorry to hear about your dilemma and the engine
I'm inclined to believe that you may well have broken your piston due to the all that weight you were carrying at the time, just too much stress on the engine and over time it caused it to fail, but I'm no mechanic so I could be wrong.
Wouldn't a broken piston have shown up on a compression test?
The Verado's are great engines, super powerful, smooth and ultra quiet, plus they look dare I say dead sexy! If you prefer to have the option of doing some trolling on your main engine go with the Verado or a four stroke, after testing the Direct Injection technology that engines like the Optimax use I still think they suffer for extended periods of trolling at lower rpm's. Yes they are very very fuel efficient, more so than four strokes in areas but overall I think if you can accept the extra weight of a 4 stroke I would go with that.
Seems like you want to stick with Mercury, but if you're looking at something else the Suzuki 4's are excellent as some of the forum members can vouch for.
I see the six cylinder Verado's all appear to weight the same 288kgs across the range regardless of hp (200-300hp) but I believe your boat is rated for a max hp of 200? Any particular reason you want to go from 200 up to 250 aside from because you are a speed freak?
The engine you were using weighs around 212kgs according to what I could find on the net, so I'd want to be sure that the extra weight on the transom wouldn't be an issue, you wouldn't want the transom cracking.
Does the engine come with any Smartcraft gauges or are they all extra? Everything I read about the Verado's say they're sweet and give very little problems, but I would still post on the US forums like hulltruth and hope you get some decent answers to guide you.
The 250 Optimax weighs 229kgs with a 60amp alternator whereas the Verado runs a 70amp version. Also the Verado has Digital Throttle & Shift so you'll most likely need a new throttle control box to benefit from that.
At least we got that water out