Your problem might be wider i.e. at the exchange it's almost certainly a contention problem of some kind, just not so sure that it is a contention problem in your house,
you may be really close (in telephone exchange terms) to a lot of big downloaders and that might be the main problem but really hard to tell.
It also might just be an intermittent problem where you are having trouble connecting to the DNS server of your ISP who knows :( internet connections at the street level are a black art these days
I am lucky I get 13MB down and about 750K up pretty much consistently.
Jim