Most trains today actually run slower than their 1920 version on the same track. We invented high speed rail in the 1960s which of course goes much faster, but most trains are not high speed and most operators of regular lines (including subways) have slowed the trains down.
My brief googling suggests this is not so in the UK at any rate.
>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
Fair enough. There is a certain romance to crossing the atlantic by ship, though. That's been on my bucket list for a while - IIRC a ticket is on the order of $1-2k for a weeklong journey from UK to US.
The round trip idea is unlikely to work well unless you're willing to wait awhile as the cruise ships are repositioning to handle specific seasons (e.g. Northern Europe in the summer, the Caribbean in the winter).
The exception is the Queen Mary II, which is an ocean liner that still does regular trans-Atlantics.
If you can afford 2 weeks off for a round trip, you should really take at least a week in the country to arrive at to see it. Cruises are nice, but you don't see the culture of the places you go. Either fly back, or take more than a two weeks. I recommend fly back, the one way trip is a once in a lifetime thing, but the return trip seems like it would be repetitive (having taken several cruises, though none trans ocean)
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.