I mentioned it in another thread (but neglected to update this one, sorry) that a removal and reattachment of the cable and attenuator to my Superhub seems to have fixed the issue I had. Speeds are now consistently high and stable.
I uploaded 2GB of photos to my Skydrive yesterday, all very painless with the 10Mb upload rate.
I'm (back to being) happy with my service now. Hopefully it will remain that way