The information that I posted about the ‘Use intelligent stream scanning’ option was given many years ago by one of the very senior Avast Team, so I don’t believe he would give that advise if would but you at risk.

How I see it is a case of when the content downloaded is scanned (not if it is scanned or not); in little chunks as it is downloaded; or when it is completed.

I have pretty much the same internet bandwidth with my BT Fibre Optic broadband on this XP Pro desktop system (so even earlier than Vista) and I haven’t experienced this. I also have a win10 Home x64 laptop using wifi on this connection. I also have a win7 SP1 netbook that wouldn’t pull the skin of a rice pudding and that also connects using wifi.

All of these systems have the ‘Use intelligent stream scanning’ option enabled and no problem, I’m at a loss as to why you are having this problem (so perhaps Vista could have an impact).

I don’t know if you have checked your laptop air intake/exhaust cleaned any blockage can raise temps forcing the fan to work overtime.