Did you ever get a solution on this?  I have a client using AVG and they are upgrading to Sage Standard 2013 and I would like to avoid any issues.

Nobody replied so I guess It's just my problem.  Honestly we are planning to move up to Advanced which I'm hoping will fix all of our speed issues.

The speed of Standard aka MAS90 is almost entirely dependt on your network hardware. Do you have gigabit servers, cables and cards? I would start there.

For me, yes my entire network is gigabit.  For the AVG problem I can solve it completely by uninstalling AVG, and my load times drop to the standard ~5 second loads.  With AVG, no matter what I do with the settings, even if I disable it, 7-9 seconds every time.

With MAS90 even if you exclude the entire mas90 directory on the server you still need to make sure the client on the workstations aren't scanning the mapped drive.  That's the most common AV performance issue with MAS 90.

Client side Script Blockers can cause odd issues too and can be a real pain to shut off.  

If you are sure its the AVG antivirus causing the issue, you could contact AVG for some guidance or perhaps post to the AVG forum.  http://forums.avg.com

If you are able to resolve please let us know.