I suspect the current cards suffer a fair performance hit with AA enabled. If this is something you can't live with then, and only then, might you want an upgrade.
Be warned, though, it will be expensive, to get any useful performance improvements you'll be looking at the 660Ti/HD7950 as a replacement.
Overclocking the graphic cards will certainly help-and it's free.
Oh yes, one last point, that i5 of yours is really, really, screaming out to be pushed harder
. Go on, get the overclocking whip out on that lazy slug as well!