I can't answer this anymore, neither in a positive or in a negative. While I was happy with the transfer rate and the "relative stability" of the line using that firmware version, I still had troubles with deterioriating line values. Over the span of about two weeks, the SNR would slowly but steadily go down to the point where a resync was forced. This seems to be a general problem with Lantiq modems, not just with a specific firmware, I have seen reports of it happening even on AVM firmware unmodified Fritzboxen.
For several reasons (one of them wanting to upgrade to 802.11ac WiFi which the Lantiq devices cannot provide) I then decided to switch to an external Broadcom-based modem + router combination. In my case that was a dirt-cheap used Zyxel VMG1312-B30A (and a Netgear R6220). This setup has been rock stable, with excellent -- and more importantly, dynamically recovering! -- line rates, for the last six months, to the point where it ran into an amusing bug where the reported uptime tops out after slightly less than two months. I don't intend to go back to a Lantiq modem anymore.