More news on general poor ADSL performance
Zen Internet has published some information from BT Wholesale in our forums, see here for the full info.
This information addresses why choosing an MTU of 1458 for your connection results in better performance for a large number of people. The problem has been traced to the BT Remote Access Servers (RAS) that are Cisco based. Apparently if the packet size is less than 1458 then packets are simply passed on, but if the packet size if greater than 1458 then packets are inspected and eventually forwarded. Normally this is no problem, but at the busier times of the day this extra work on the larger packets can overwhelm the RAS servers and cause the slow downs that people are experiencing.
See this news post for more information on setting your MTU. For users that use Dial Up networking, then DrTCP is the simplest tool, and usually setting the Dial Up (RAS) MTU will fix things (this applies to most USB modem users).
If unsure about any of this, then consult the forums for advice from other users.