Hmm the great single vs multi debate. Yes multis are more expensive to operate. Actually a good rule of thumb might be take the cost of a running a Bonanza double it and add another 20-30%. (that's what old man Rimmer reckons and he had various Barons over a number of years) . Twins have a lot more plumbing than the equivilant airframed single dual vac etc etc.
There are those that argue that singles are safer (this has been covered extensively in other threads...). I'm not sure that they are in a apples with apples comparision. Just a personal view but I reckon most asymetric twin accidents are as a result of, first up rusty skills (stall/spin or below MCA departure), but also a belief that a light twin will behave like a Perf A type. Seems to me that once you desend below your decision height with one out you need to have a single dead stick mentality - (ie it's better to put it anywhere within the airfield boundry at low speed under some kind of control than to be inverted and nose down and being just along for the ride...but I digress...)
I think you have to ask yourself the question what is my mission? As you've discribed it you are looking for year round ops to a timetable.
That means full airways and de-iceing are musts (or more acurately anti-icing capability - most heavy singles and light twins de-ice can't handle flight in prolonged icing). Evern if they don't hav it fitted all Barons are plumbed for boots whereas Bonanzas aren't
You want a high alt cruise (relatively) capability (I read somewhere that 95% of the weather is below FL150). In effect that means turbocharging and either pressurisation or an O2 system
You want to have long over water sectors so maybe there is peace of mind in having two donkeys either that, or it's chicken route time - for my money anyway.
If it was me and all other things were equal (ie money which of course it never is) I reckon your choice might come down to either a Baron 58TC or P58 then again maybe a Malibu Mirage. (though the latter would have me wanting to shorten the over water time).
Just my opinon though...