First up is Futuremark’s
3D Mark SE in our line of bench tests. I ran a batch with both no anti-aliasing and 4X AA to compare how much of a hit the card takes when the process is activated.

And here are the scores with 4XAA turned on.

There is a mighty big drop when turning on anti-aliasing to generate a cleaner edges. With a loss of 3000 to 5000 3D marks depending on the resolution, it's probably not worth the speed loss to activate the feature for games.
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