http://www.firingsquad.com/hardware/...0xtx/page7.asp You always max out everything you can when benchmarking as you are again maxing out the card and driver's abilities. If the case of this old Radeon hardware we KNOW what the hardware is capable of, so what we're seeing with these tests is what the Gallium3D drivers are capable of making the card do since we are still far off from what the hardware is known to be capable of.
The vast majority will run the game at their LCD's native resolution with all settings maxed that they can get away with before looking at what they can do with AA settings. your goal with AA is to reduce jagged edges, if you are lowering the resolution and using lower detail levels on the textures then even with AA turned up it's going to look like crap.
Performance tuning though would be playing with the settings of the usual biggest performance impactors like soft shadows, dynamic lighting and AA settings since AF settings are almost free on GPUs from the last 5-6 years.