If you are getting a true 7.8Mb/s download speed you are among the fortunate few since the advertised speeds of lots of ISPs of
" UP TO 8Mbytes/sec download speed"
are rarely achieved in practice due to signal /noise, signal attenuation and other line issues. BT systems have a semi automated line monitoring system which down regulates your data transfer speed to what it decides is a "reliable" speed to give you good connectivity. This is often more like 3-4 Mbytes/sec rather than the advertised " 8 Mbytes/sec"
This "UP TO 8Mbytes/sec" phrase is misleading advertising IMHO and should have been banned by THE ADVERTISING STANDARD AUTHORITY
Theres a good speed test at
http://www.myspeed.com/pe/index.html free download which can tell you about connectivity to servers in the USA and UK.
I suggest you try that. Theres another good speed tester here
http://www.thinkbroadband.com/faq.html but needs the java plug in for whatever browser you are using. As has been said there are lots of other factors involved including internet traffic and site server response etc etc.