OK, lets ignore the pings for the moment. Can you be more specific about the speed tests? My experience is they are at best a 'guesstimate' on the higher speed products, use 4 different speed test sites/servers you will get 4 different results. (see my post a few days ago in this thread)
I'm also of an opinion that there is some marketing 'fluff' of the products, eg the Zen 900 residential package says '900Mbs Average Download' I think that is open to interpretation, my interpretation is that is a maximum speed of the product.
The speed tests are done from the Speedtest.net CLI tool in the case reported above, to Zen's own and Swish Fibre's servers. These are the same test servers as you can access at
www.speedtest.net, and they do perform as you would expect in the presence of an unencumbered internet connection and a home network that is so capable. I used the command line version as it was easy to script and run repeated tests over and over, but you get basically the same results from the web browser. @skyeci has already shown his connection now is performing how mine was prior to the Zen GEA migration event (ie achieving over 900mbps to Zen and Swish fibre servers). I am unable to get those kind of results since I was taken off BT's backhaul from our exchange to Zen, and put onto Zen's own backhaul from our exchange to Zen. The change is absolutely coincident with the very characteristic change in the ping graphs.
The average is clearly not the maximum speed of the product. It's frequently possible to achieve in excess of the 900Mbps, and I have most of the time via those speed tests. For it to be an average, unless everyone achieves bang-on 900Mbps, literally the definition of average means that some will be above 900Mbps to counterbalance those below, hence it could never be a maximum.
If some are going to be achieving just 450mbps per the speed guarantee, for the average to hold, most will need to be above 900mbps. For every one person at 450mbps you would need 45 people at 910mbps to hold an average of 900mbps (I was usually at 912 or 913mbps), or 22.5 people at 920mbps, or 450 people at 901mbps, etc etc. You get the picture.
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I'd be flabbergasted if it turned out to be a PON issue give that the change was coincident with the backhaul change and the visible step change in TBB graphs indicating some significant change in the network between me an the TBB servers thanks to that change. Not only that, I'm pretty sure there is max one other person on this PON at the moment (I can see all the CBTs), and you'd be very unlucky for 1) that person to also be on 900mbps and 2) be constantly maxing out the connection. Of course there are other PON possibilities like a rogue ONT on the PON, but again the circumstance of these changes just seems to make such things very unlikely causes.