Am I stuck with 4000mb?

[#1]

That’s done the trick, line speed is now 4.5 MB.
What’s the most I can hope for should I leave it at that or try another reboot and hope for 5 MB?

[#2]

I would leave it for a couple of days, if it stays stable over that time then give it another go.

[#3]

At the risk of barking up the wrong tree, is there any chance of bumping my line speed from 4.5 to 5.0? As my line profile has been around the 5.500 mark for a week now, and yes I have resynced the router.
Funny thing is my speed test was giving me 5.200 before the weekend despite my line speed showing 4.5 but now it’s not going above 4.5.

[#4]

I've changed it to 5200 though the delta reports are still coming through at 4500 and will continue to do so until the remainder of the quantization project rolls out - basically that'll mean when we do get a new delta report through your profile on our side of things will be set to match.