Thanks - got it; and you're in sync at 80 Meg and interleaving is not applied to your line, so any issues you're seeing aren't down to any profile issues on your line.
It may be worth rebooting your router, maybe specify DNS
to see if it's DNS lookups coming back slowly from the router (if it's serving as a caching DNS server for your network).
I don't know what your technical proficiency is, so other things may be obvious stuff that you've tried already - but it may be worth seeing if it's related to particular software/browsers being used when you see issues (on my Mac, Chrome or Safari can sometimes slow down, so closing the application properly and re-opening - rather than just closing windows - can help).
ZeN Performance and Process Improvement Manager