Purple:
I'm sure Lu can tell you much more than almost anyone here about safety.
One point worth thinking about tho. If an engine fails it might not mean it simply stops developing thrust, depending on *how* it fails it could cause damage to other critical parts, eg the wing. It is arguable therefore that 2 engines are safer than 4 as there is less chance of an engine failure. I believe that Lindbergh had this in mind when he crossed the Atlantic in his *single* engined aircraft.