I don't know what might be going on with your system as I haven't suffered any issue with the rootkit scan and my system isn't particularly fast but the rootkit scan should take seconds rather than minutes.
As Vlk said he couldn't see anything suspicious in your dump file.
Unfortunately I can't really offer any other suggestions (other than what you are doing to disable the rootkit scan on boot/just after boot), being just an avast user like yourself.
How long does a rootkit scan take if you initiate it manually ?
ashQuick.exe rootkit scan - Using the windows, run, type or copy and paste the command below including quotes.
"C:\Program Files\Alwil Software\Avast4\ashQuick.exe" "<RTK>SUPERQUICK"
