Ramjam,
You haven't provided any details about your computer, CPU Speed, Ram Size, Operating System. With fast processors, plenty of memory etc, the increased checks needed by AV to combat the ever increasing number of threats does not generally impose a significant reduction in performance, but that is not always the case with older, slower systems.
If you are not using instant messaging, Microsoft outlook/exchange, or P2P I would terminate these shields simply to perhaps save some memory - you can always restart them if you want later.
As you specifically referred to surfing, you could try terminating the Web shield. This will remove a layer of protection, and you will then be relying on the Standard shield, so understand if it does improve your surfing performance, it is at a price, and you must decide if it is worth it.