That seems to be more than I have noticed before, could that be sign of a problem? Knowing myself the following observation may be irrelevant to the above.
On a few occasions recently my sync has been excellent for the SNRM and attenuation (8200+ and 888 kbps),but sometimes a resync (involuntary) can reduce downstream a little but more so on the up e.g. 888 to ~ 600 kbps.
(Apologies for this being a steam ADSL topic)