I think it may just take a little time to fully take effect after disabling it.

The first time I checked, it was %PPA is disable but %PPA WAN entries was 1

All seems normal now, so false alert I guess

I have had big problems with this firmware update, internet was almost unusable (like being on dial up in the 90s... WHOOOOOOOOO!!). After reading this post, I have disabled hardware acceleration and all is back to normal.
Thanks

What I want to know is why is my upstream sync speed so much better than what is typical for me with the 3.8.4_STD firmware using the modem code of 548006_A/B/C HW: A.

Hardware, Firmware, Service compatibilities and incompatibilities I'm guessing

Draytek have produced several versions of the this firmware upgrade and presumably for good reason and probably because different ISP's use different hardware and therefore different firmwares for there own hardware containing different modem codes.
So our hardware and it's firmware has to communicate with your ISP's hardware and its firmware and modem codes.

I'm assuming that if they are not wholly compatible then we experience problems online.

By trying different firmware versions we find a version that best suits our ISP's service. An firmware option that's compatible with someone connected to a TalkTalk service may not work properly with someone that's connected to a Vodafone service because the two companies may be using different hardware and modem codes.

For whatever reason the STD firmware for you is better than the BT version but it may very well be the opposite for somebody else and maybe because of an incompatibility with the ISP's hardware at the other end.

Thanks, that's a very good description of what is likely to be happening in this case.

It is a notable difference so I recommend that the original poster contacts support to investigate the difference (if you want to) - it's likely to be specific to your ISP's exchange / cabinet VDSL equipment.

It would likely be useful for the support team to understand scenarios where the older non-vectoring modem code could give better results than the modem code that supports vectoring.

Not 100% sure, but think the DSLAM in my street cabinet is of the ECI type, the other popular type in the UK being Huawei. I know my old BT Openreach VDSL modem is a ECI B-Focus V-2Fub/r Rev.B

Are you saying for me to contact Draytek support or my ISP, I doubt my ISP (Plusnet) will offer support for non ISP supplied hardware. Even when I used the BT Openreach modem, i was only getting 5-6Mbps up during the last year if using it.

My upload speed slowly dropped from 13-15Mbps up to 5-6Mbps up during the first couple of years of getting a fibre service in 2013 what I have attributed to increased cross-talk with the VDSL service becoming popular.