I am considering going to Iceland and was wondering if it is feasible to take there my car with me. The only way to get there by ferry that I could find is described here, which suggests getting to Denmark first (which is in the opposite direction), and then getting a slow ferry from there. Is there a better way?
The only ferry to Iceland is the weekly ferry from Denmark. It takes a while and you spend two nights aboard each way (and incidentally get the opportunity to visit the Faeroe Islands along the way).
The ferry is not guaranteed to run during winter (it mostly carries cargo during the winter months, if there is cargo going to Iceland you can book a trip, but only shortly before departure).
The ferry is also rather expensive, so for a short trip (anything under a week certainly) you would likely find it cheaper to fly and then rent a car. This will also save you 4 days at sea, which would eat into any shorter trip.
The only car ferry to Iceland leaves from Hirtshals, Denmark, so you have to somehow get to Denmark first. So the fastest way is to drive to Dover, take the Channel tunnel to Calais, then travel over Antwerp, Duisburg and Hamburg to Hirtshals. There take the car ferry to Reykjavik.
London→Hirtshals takes approximately 14 hours.
Hirtshals→Reykjavik really depends on the weather and the season, but you should at least calculate 80 hours.
It also depends on the further development. Until recently, you had to wait two days on the Faeroe island. But this has changed, but it is not sure if it will be so in the future.