>Some trains, such as the famous "Flying Scotsman" in the United Kingdom, were able to reach speeds of up to around 90 miles per hour (145 kilometers per hour). However, this was not the norm and most trains had a top speed of around 50-60 miles per hour
They are quicker now - 130mph, 80 mph is normal
The exception is the Queen Mary II, which is an ocean liner that still does regular trans-Atlantics.
Of course both Europe and North America are large continents with a lot more to see than you can do in a week, but few of us have the budget to be a world traveler for a few decades to see everything.
Right, the point is it might be six months, since a lot of cruise lines will do only one crossing for northern/southern hemisphere summer toggling.
e.g. here in Seattle the cruise ships that go between here and Alaska make a single trip down to Australia or somewhere in the fall, and then don't come back for half a year.
So yes, like you said - probably fly back.
I think you can get a ticket for less than $1k,though you'd probably be cramped with no window.