They are more conservative on noise margins for many connections so that may lose you some speed. What are the stats on Sky and do you know what they were on Zen?
EDIT : Also, might be that sky is defaulting to ADSL2+ which may be slower than ADSL on longer lines. Forcing it to ADSL may gain some speed back.
Edited by ian72 (Mon 09-May-11 14:16:06)