but even with a TBM850 - would you feel comfortable doing a 4hr leg over water? I wouldn't. But I would in a twin.
That is however an illusion. A SE PT6 is about 5x less likely to go down than a piston twin. But hey we have been here before
The other thing is that there are very few 4hr legs over water - unless you are doing an Atlantic run and a pretty direct one. 4hrs is about 1000nm+ at economy cruise.