I decided to just try it plugged it into the ISP BTHH5 to skip the PPPoE function. So I factory reset and let it connect to the BT HH5 ISP router (I also put it on DMZ for belts and braces, although it was working fine without this.
It seems to be working just fine, but needed a reboot to apply the downstream QOS %.
I get my original full speeds with QOS enabled. 68/18 - 68.5/18.5 (the same as if straight from the ISP router) and with <70ms lag spike with no Buffer Bloat
When I set to 70% the Download Buffeblost didnt work but the upload one did. I tried updating distribution, adjusting but I just couldn't get the download to work. And kept getting messages in the system:
kern.warn kernel: [ 1425.380000] HTB: quantum of class 10002 is big. Consider r2q change.
Then I rebooted and it worked:
Then I tried adjusting the % sliders and got the quantum of class 10002 is big. Consider r2q change message accompanied by an iffy download result:
Then I waited, changed nothing and tried again and got perfect result:
And it all seems to be working Perfectly, here are the dslreports, (which before when it went through PPPoE I always had some random 150-180ms spikes early on in the download***edit - I still get the spikes, BUT only when logged into DSLreports and using finer sample rates setting, i think this is bug with dsl reports****)
So, I think, the problems, as mentioned by support, are all to do with the PPPoE. So, I'll use it through the ISP router and put my shiny new £85 modem on the shelf ready for another day or maybe an XR300 or XR500. I hope it continues to works once the network has more devices and comes under heavy load tonight.