To those who get this on Aquiss and have set PPPoE at 1492 in their Windows TCP/IP Stack, be sure to change it from 1480 (default) to 1492 in the router, I noticed whilst speed tests were fine, download speeds themselves were 'iffy', luckily a quick search found the issue, mismatched MTU's - soon as I changed it the problem went away
so yeah these TP-Link Archer series seem to have 1480 MTU by default.