Any known issues with 2860 running 3.8.9.1_BT on Sky Fibre?

I just upgrade from the 40Mb to the 80 Mb service- both Draytek and Sky Q routers ran full rate on the 40Mb service. On 80Mb service the Draytek trains at 57Mb, replacing it with the standard Sky Q router I get 63Mb with same cables/ positioning.

Both show 15dB attenuation with 6dB SNR.

Have tried cfg rst/ restore and both 576d17_572801 and 574307_571801 Annexe A modem code options- no difference. (576D17_A/B/C HW: A chosen if I leave default)

Had small differential before- but this is too significant a drop to live with.

Thanks,

Chris