I once went to a talk by a doctor who flew on a Twin to Antarctica. His comment was that the pilot didn’t bother wearing any immersion suit as he considered it wouldn’t help.
You won‘t get any real replies. It‘s mostly a matter of personal decisions, often irrational. And that‘s fine.
Also, often the main reason for carrying this stuff is not because it will actually help you in the circumstance, but that it allows you to stay more relaxed and sleep better. It‘s a with tiedowns. Will they really help in case of a major storm? Probably not. Will they allow you to sleep better when on tour? Quite.
His comment was that the pilot didn’t bother wearing any immersion suit as he considered it wouldn’t help.
I think that’s completely daft – like the old saying that if you get an engine failure at night, don’t switch on the landing light because you might see something you don’t like.
The main issue on that run is that you are very far from rescue, and some large % of pilots are never found. Old ferry pilots have lost many colleagues up there. In the very cold water, an immersion suit is necessary because if you don’t get into a liferaft right away and dry (which is possible but it’s another “what if”) you will get too cold very fast. Also I hear that the countries up there send people large bills for pulling them out.
I’ve been told by many people that I should do the N Atlantic run but even though my plane could easily do it (1300nm range to empty tanks) I’ve never been interested because of all the hassle, and the 30+ hours one spends mostly utterly bored. And then you have to it all again on the way back 
The most important equipment is a PLB. Without it it is very difficult to find a liferaft let alone a person in a lifevest floating in the sea.
I agree that a PLB is critical – that will hopefully get the SAR to your location. Per post 78879 above, an SAR crewman once told us that the single most important thing (from their POV) is for you to have something, like a liferaft, that will help them spot you. It is very difficult to spot a man in the water from the air.
I do know a former Nimrod pilot who actually spotted a “man overboard” fisherman in the water. He considered that to be a million-to-one chance.
As for N.Atlantic crossing in an MEP, we left our immersion suits ready in the back. Logic was that we were at +FL250 and there would be plenty time to put them on as we contemplated our impending demise
I’ve been told by many people that I should do the N Atlantic run but even though my plane could easily do it (1300nm range to empty tanks) I’ve never been interested because of all the hassle, and the 30+ hours one spends mostly utterly bored. And then you have to it all again on the way back
Thought I’d rise to the bait 
The reason is, you get to see stuff like this:
And then you get to fly your own plane in Canada and the USA and do more stuff like this:
I had the impression in slow SEP/MEP you have a high chance of ditching but also high probability to survive the ditch, so the question is mainly how to improve your chance of getting rescued, say an extra day for someone to find you in the middle of the Atlantic? the puzzle is that 4 out of 5 GA ditches deep in Atlantic/Pacific were survivable and people surpisinly got rescued in time, no idea how much of this is attributed to gear & equipment & skill (same number is observed for surviving & rescue of ditching near the shores)
In the other hand for fast twin jets/turboprops, the probability ditching is nil, so the probably to to survive a ditch, but would be fun to see 300 passengers wearing immersion suits and open life rafts before takeoff
Don’t think many airliners had survivable landing on water instead of uncontrolled crash? also not that many at all were in deep Oceans (maybe this one https://en.wikipedia.org/wiki/ALM_Flight_980 ? or this one Flying Tiger Line Flight 923?), while most of ditches happened near shores after takeoff (Sully, highjacked Ethiopian Airline) and surely almost none was a serious aircraft reliability issue…
Nice
One veteran (just celebrated his 100th ) used to fly Islanders to Stavanger from the UK, he didn’t wear safety gear. Another veteran of North Atlantic crossings in SEP has the full kit (immersion suit raft) from Wick. Don’t forget the rifle for Kulusuk.
Personally, I think the key is you will never have the situation fully in control in a ditching.
You may think a low wing may help you board your raft but perhaps the swell or the touchdown and resulting damage may render that impractical.
You may think the nicely equipped heavy raft will save you but then it may be too bulky to manhandle in an actual situation
You may think the high wing will do a safer touchdown but then you could end up misjudging the flare anyway
You may think the life vest will be useless cos you will get straight into your raft, but maybe you will first go into the water by accident
…
Bottom line: significant overwater distances to me mean life raft AND full time vests on. No fiddling inside the airplane. I chose a light SP raft with heavy emergency equipment. I find it reasonable to manhandle for me at about 12 kg total. Bulkier, heavier ones I do not feel comfy with. I have found Enclosed vests rarely (in my case never in 15 yrs and I almost always fly with pax and overwater) get damaged in the average full-time wear use.
I have practiced boarding the SP several times with my usual pax and find it very accessible. Admittedly that was in a pool but we have developed a fairly reliable technique which involves two people. Three better for stability. Once one is onboard the rest are easy.
This way we feel we have more options open that if we only went raft or vests or hvy raft.
This study from 1996 shows at the end typical survival times in the sea.
