I had an upstream issue. It sank to 384kbps, then further down to 256kbps. Eventually it was solved by replacing the filtered faceplate, at least I think that was the cause. Matters improved afterwards. I can only think that a duff component in the discarded faceplate was introducing noise which affected the lower frequencies that the upstream signal uses.
I now use a clarity.it modified BT faceplate.
I would imagine that upstream speed variation only has a very modest effect on ping rate, especially since ping data rates are probably low.