Well as explained inthis topic you have nothing to worry about.
The term decompression bomb is more scary than what it is actually reporting, that the file is highly compressed and if it were unpacked for scanning it would be exceptionally large (par for the course of a large movie file) and for that reason alone avast hasn't scanned it, no other reason. How could it determine anything, malicious or otherwise, as it hasn't scanned them.Files that can't be scanned are just that, not an indication they are suspicious/infected, just unable to be scanned.
So deleting those S&D files was wrong.
So I would say these files have nothing to do with your other issue with IE slowing down, that is likely to do with other undetected malware.
If you haven't already got this software (freeware), download, install, update and run it, preferably in safe mode
and report the findings (it should product a log file).