Morphological antialiasing is similar to what super eagle does, it operates on the final rendered 2d frame so it can't distinguish between polygon edges and font edges.

I am confused with the OPs use of "amd overdrive", the settings he mentions are in the driver control panel.

As for why it would kill the benchmark performance, since a few driver releases ago you can't force antialiasing (not sure if it cover morpho) on the game anymore (it's in the driver release notes) so it might be the case that the game is ignoring the extended settings but the benchmark isn't.