You state you have been infection free for the past 3 or 4 years despite testing malwares. During the entire time you have been using the combo. In my estimation you have no need to change.
I would bet that Sandboxie is the primary reason your system has had no persistent infection. Outpost and Malwarebytes provide a decent base-line protection.
If you start to think that you can somehow create an "Impenetrable Fortress" then you will do nothing but drive yourself nuts and be bitterly disappointed in the end.
I am an adherent to the anti-executable + virtualization + outbound firewall protection model. If you want to further lock-down your system I would recommend the freeware anti-executable NoVirusThanks Exe Radar Pro. It is light on resources and the user interface is easy to use.
Unless you are experiencing performance or compatibility issues then I can see no reason to change your config. If, on the other hand, you are bored with it, well, I understand why you would want to change...