Another quick update after 2 full days is that Version 6 running slower on my doc's desktop when she doing her e prescriptions.
This means now AC has to compare hers against its med database to satisfy one of those meaningful use requirements. For front pcs, our staff haven't notice any differences.
My IT background a long while back was also in software development. Seems that AC code development evolves thru time by change its underlying coding and but not entirely redesigned from scratch. Inherently that would not be the most efficient way to go but ok for now. If one user could feel its degrading performance then we have to wait in patience as not much can be done till next version, probably 7.
So for those AC users who have not adapted to the the AC6 and have a larger collection of data definitely need to upgrade their server to a more powerful one before doing their upgrade.