Not a startup issue with Mbam and avast! (maybe XP), as I've experienced freezes when the sytem has been running for a couple of hours (and overnight).
I did, at first, have freezes immediately after logging in, even before the login screen disappeared, the system would freeze; that seemed to settle down, then random freezes would occur.
Wish I had the time to troubleshoot more with avast! 5, but I need to get a lot of work done and a random freeze has already cost me 5 hours or so.
So I'm back to 4.8 (though there was also difficulty uninstalling v5).