Version 8.0.2 is being used by many people and seems pretty stable..... I think you will not have any major problems and I have been amazed that AC has not done this before - trying to support 5 different versions in support is awful.
I would agree with Steve and would recommend that anyone on earlier versions at least download and try V8 to get a feel for what has been added.
That said, there is still a speed issue compared with V6, but not that serious. Not much speed difference with V7.
