Just been reading this thread and there are a few things I would like to address. First of all, for reference, I'm studying in the UK, but I grew up in Holland, and know a thing or two about the Dutch university system through information we got at school and through my friends from secondary school who are now studying at Dutch universities.
My first point: I feel like there is some scaremongering going on here (not going to name any names). Holland is not the other side of the world, you don't need to worry at all about half the stuff you've been warned about. English is the least of your problems, London to Amsterdam is a 45 minute flight, so if you do feel homesick, you can go home for the weekend, etc.
As for the workload, I don't think it's harder than Britain. Most of the students who drop out do so because they themselves choose to (because they don't like the course). A lot of people in Holland make little effort to properly choose their subject, this is the cause of most of the dropouts, not some kind of super high requirement. What you need to take into account when comparing grades is that in Holland the pass mark is 55 or 60 out of 100 on an exam, the 80 you mentioned may refer to 80% of the total number of points you can get in a year. I'm not 100% on how those work, but I believe passing the exam means you get the points for that subject, which would mean that you need to pass at least 80% of your subjects in first year. Another thing I would like to mention is that it is not uncommon for students in the Netherlands to spend an extra (half) year doing the course if they need extra time to complete their degree (check your uni's website for this). Of course, you'll want to do it in the normal time, but I'm just trying to say that Dutch unis don't really do the whole kicking people out thing so much.
As for the Amsterdam vs Groningen issue, the pros and cons I would like to mention are:
Amsterdam:
Pros: near the airport, near many other major cities, big city, good uni, lots of foreigners, lots of culture
Cons: most expensive to get accommodation and accommodation is hardest to find (Holland doesn't have halls, it's all private or fraternity (which I would not recommend)), big city
Groningen:
Pros: nice student town, good uni, accommodation should be easier to find and cheaper
Cons: relatively far away from other cities/major airport, not the most international part of the country (though you'll still get by fine even without Dutch)
Hope all this helps, feel free to ask any specific questions.