For me, even AAx2 made a significant difference.

Without any AA, there are a lot of jaggies on my character, especially the arms. Just bumping it up to AAx2 made a significant difference. There's still a little bit of jaggies, but it's much better, so I'm sure that higher AA would be even better.

It would all depend on your systems performance. If you can, there's no reason not to, basically.