It all depends on the day, and the weather. I personally have yet to cross the Atlantic in the Stratocruiser (an engine fire and prop pitch loss both contributed to turning around twice), but have done it in other jets. I have however, crossed every other ocean so far in my round-the-world flight, so I'm no stranger to the long, over-water operations. I have, so far, lost two engines over the ocean. Today, trans-atlantic tracks are created every day, to space all flights crossing the ocean. As you can see on the below pictures, trans-Atlantic tracks are plotted across the ocean, ensuring that there is 60 miles lateral spacing between aircraft, and thus planes fly at a range of altitudes on those tracks. Those tracks change daily, and are setup to, as I said, space out flights for the 60mi+ lateral distance, and offer the best route for the winds that day.
Tracks A and B are for the real long-range stuff like Salt Lake City, San Francisco and Los Angeles. C, D, E, and F are all for New England-Europe.
As you can see from the Upper Air weather, flying East to West on this particular day (this is from March 18) would have significant headwinds at FL300, which would normally be optimum for fuel consumption and long-range operations.
Gander is now an alternate on Trans-Atlantic flights, seeing that jets can do the whole thing non-stop. There are several alternates to keep in mind: Shannon (EINN), and Reykjavík (BIKF). Another airport exists, called Dyagilevo UUBD. It is a Russian base, with a 9,000ft runway and belongs to the Russian military. In an emergency (like two engines out) you could land there. Technically, Dyagilevo is in mainland Russia, but FSX has put it in the mid-atlantic, so you could land there, but going off the runway means falling 200ft into the ocean.