Hello!
Should read "most knackered old training type twins..." I agree the BE76 or Seminole have pretty crap SE performance.
Our flying school Seminole (non-turbo!) easily maintains 6000ft on one engine. With the exception of the Alps, you can fly anywhere in central Europe at that altitude. And other than with some more complex twins like the C340 or C421B, all the fuel on board is available to the remaining engine, so longer overwater flights can safely be completed.
At this time of the year with poor weather and early darkness, I feel much safer in the lightest of light twins than in any piston single.
Greetings, Max