I installed MSE yesterday just to test it with Avast! Home 4.8 (on XP SP3) and it caused my system to hang majorly. Everything took at least a minute to open and it took me 2+ minutes just to get into Control Panel and uninstall it. So for my system at least 4.8 and MSE do not like each other at all.
What is your system CPU type and speed plus how much RAM does the system have?
E5200 2.5GHZ, 4GB RAM, 320GB HD, Windows 7 Home Premium 64bit, avast! V8.0 Free, IE10
P4 2.8GHZ, 1.5GB RAM, 40GB HD, XP Pro SP3 32bit, avast! V8.0 Free, Google Chrome
with hpHosts, MVPS HOSTS files, SpeedFan, WinPatrol PLUS