I've been running AVG 9.0 without any hassles, but I've never run 8.5. Also have installed it on machines for several friends, one of which had a virus and some trojans that Norton didn't find but AVG killed without a problem. It is resource intensive when a scan is running, so I set it to run when I'm usually not using the PC. If I am using and notice it is running it is simply two clicks to kill it until the next day.
The only issue I've had is a couple false alarms being warned about unsafe websites.