Recently crossed the North Sea in my SR-22, from North Dene
to SPY Holland outbound. I carry lifejacket, raft and EPR.
Interestingly I was not out of glide distance of a vessel
or platform for the whole ~100 mile trip though the Dutch
class-A airspace pushing you down to <1500ft is a real
pain.
I do think that if you're going to do this some experience
with instrument flying is essential as you frequently will
lose your visual horizon completely as the sky and the
sea merge in a dull-green haze.
Personally I think the latter is more of an issue than
the chance of losing your engine...it has happened to
me on three occasions in the past year.
-- Andrew