I may be wrong, but my web page load times on my PC are nowhere near as snappy as my dads page load times on his connection on his PC, only big differences are he uses Windows 7 and I use Windows 10 & he is on ADSL and im on VDSL - we both have similar PC setups, he is on a 17Mb ADSL Talk Talk connection with 21ms latency and Iam on a 67Mbps VDSL Plusnet connection with 21ms latency
It
may be down to DNS performance. I do not know how well Plusnet's DNS servers perform, nor do I know how good the HH5B is at providing DNS name resolution services (since, in most cases, the gateway is a DNS server which does its own lookups to other DNS servers). You could try some
benchmarking (add the Plusnet DNS servers in the list for comparison) or even just go straight ahead configure the computer to use
Plusnet's,
Google's or another DNS provider's servers directly.
I also get a poor grade on ThinkBroadband's speedtest - it says its a grade B for latency while downloading and grade D for latency while uploading ?? (bufferbloat it mentions)
Bufferbloat is quite common on consumer connections, regardless of speed. Quality of Service (QoS) would certainly be effective for use on the upstream by rate limiting to approx. 95% for all data. Unfortunately, for the downstream, there is not a whole lot you can do unless you are able to rate limit your downstream from the ISP's side (which cannot be done on Plusnet) to reduce bufferbloat (since data is going to be sent down the line at the maximum rate). I know the HH5B doesn't have QoS, so your only choice is to limit speeds on individual devices until you replace the router if you are noticing lag when downloading/uploading.