As I've said elsewhere on this forum,McAfee let me down early this year and I had the latest definitions hot off the web at the time!
After a complete re-format I have had Nortons watching the shop and couldn't be happier so far.("Zone Alarm" as well)
Doesn't seem to slow things down any more than McAfee did either!
40 minutes to open a file? Bigger problem than your software methinks?