A few days ago i had my ADSL extension re-wired with cat5e and it has made rather a big difference from how it was before. As it was i got a SNR of 7.5db in the day and now it is at 9.4db in the day and also the CRC errors per 15 min interval are much better also.
I can recommend using cat5e for ADSL extension runs, it makes a big difference to the connection.