Assuming you mean Mb not MB, (1 Byte = 8 bits), 5Mbps is fairly slow as you say. 20 is quite common over here and many people have ditched it for 40 or 50Mbps which is now getting quite widespread.
Regarding sites that can utilize it, most popular ones have huge capacity, but the more users that get high speeds the more they will come under pressure to increase it.
Remember that DSL actual connection speed depends very much on the line length. So here we are sold "up to 20Mbps". If you are fairly close to the phone exchange we may get that, but if we are a long way away we might only get 6Mbps.
Then there is the question you raise about the site you are reading from.
Then over here we also have a large number of suppliers (ISPs) available to most homes, and the capacity the supplier buys to cater for their customers' needs varies a lot. I think where you are you may have a very limited choice.
My view is that for a single user at home the 20Mbps is more than adequate for everything except Torrents (P2P). For a home that has parents with a computer each and 2-3 kids with one as well on YouTube/Twitter/Facebook etc all the time, or anyone doing lots of big downloads, then the faster the better.
Then there is gaming. Again, for a single user not doing a download 5Mbps is fine. But even on 20Mbps, if one user in the home is downloading a film using P2P them someone else in that home doing gaming is going to get killed.
Cable here doesn't suffer because of distance, but again the throughput can be good or bad compared to the connection speed.
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