I have stayed with AVG8, and I can't say that I've seen any noticeable performance hit from it. However, I wouldn't class myself as a power user. I don't use the PC for games (Not even MS Flight Sim!), just internet browsing and emailing. I use my PowerBook G4 mostly, and I'm considering etting rid of the PC soon anyhow, probably with a view to rationalising all my IT bit s of kit down to a MacBook Pro.
Until that happens, I'm happy for AVG8 to stay there. I did notice another thing the other day. When you use a search engine like Google, AVG8 puts a little spinning grey disc between each link on the results page. When AVG8 has filtered the link, all the "OK" ones get a little green tick next to them. This is a great plus for me, as I can say to the wife to use these little markers, rather that try and explain to how to spot safe and unsafe weblinks!