I have switched from the zyxel to the 8800nl now, and I think the nl is using an older version of the 39 dsl driver.
Some observations.
The last day or so on the zyxel I see on the mydslwebstats page I had loads of dips in my US snrm, they were not causing errors due to my high snrm, but they look worrying, at this time I am not sure if I think its the zyxel or the line. I do remember once when looking at the GUI seeing the US attainable lose a few mbit then recover again a minute after. But only just notice the graph which has many of the dips.
So far on the 8800nl I have noticed the DS snrm is higher (which probably accounts for the lower sync speed that matches the hg612) as well as the US snrm been higher as well with so far no dips. Error rates no judgement yet as the zyxel from about 8pm to about midday had low error rates as well, but recent afternoons on my connection have been rocky.