@adhawkins I've not seen any difference by disabling DNS resolver. What has made a major difference is switching my DNS provider from Cloudflare to Quad 9. I'm using my DNS as the monitor IP for the Virgin link and this shows that peak RTT has more than halved from ~50ms to ~20ms when I look at the PFSense status monitor. I've attached the monitor graph and circled the point where the change was made.
I'm not certain, but think I can see an improvement in the BQM. The first BQM below shows the link before I made the change and the second one is after. For reference, I currently have the Virgin Hub in router mode:
So I'm assuming Virgin has routing problems with Cloudflare (which wasn't always the case), and these don't affect Quad9 (or Google from my quick look). What I'm not sure is why these routing issues would affect the BQM, and how much impact they have on general web use. Maybe some of the more knowledgeable folks on this forum can help with these questions?
Next step is to switch modem mode back on and see how the new configuration copes when broadband is subjected to load on weekdays.
(Edit: would also be good to understand which DNS folks are using when we have discussion about performance so we can compare like with like if Virgin is not routing sites correctly.)
[Moderator edited to fix the links to display the two images.]