I reckon (without working it out) that a decent tourer (TB20 etc, 1000+nm range) could do the Atlantic crossing direct (Shannon-USA) in either direction (usually W -> E is much better wind-wise) if fitted with a really big internal fuel tank and the rear seats removed.
Whether this can be done legally I have no idea, and the engine failure options aren't appealing, but they are only marginally more appealing on the northern route...
In reality, ferry pilots fly such planes via the usual northern route without ferry tanks. Much much simpler paperwork-wise; just plan the flight, wait for reasonable weather, jump in and go.
I believe the DA42 did it in the "easy" direction. Not sure I would have done that, having read the usual stuff about the Thielert engines...