I believe that flying over water in a SEP is very personal and depends on your own level of comfort. The engine doesn't know what it is flying over and I'd prefer it to quit over water than when I'm crossing the Appenines
I flew nearly 15 hours over the Mediterrean Sea last year (summer months) with life jackets, dinghy and personal ELB (watch) and was perfectly happy.
I wouldn't be keen to do so during winter.
Funny enough, in December flying over the Indian Ocean during circuits at Durban I felt quite uncomfortable, even if we were near the beach.
This thread has got me thinking: I'll double check all equipment on future overwater flights.
Ciao,
AE