Odd issue with AA & Doom 3

[Lazlo Panaflex]

I recently played through Doom 3 @ 1600x1200 HQ (no AA) on my C2D 'rig in the sig'. Timedemo = ~123 FPS. When I tried to run the game at 16x12 HQ, 8X AA, the framerate took a huge hit...~22 FPS! The mouse cursor is kinda jerky as well. WTH? I was under the assumption that my system would handle AA at that rate w/ no problems...any thoughts? (Driver ver is 93.71).

(btw, Far Cry runs fine @ 16x12 max settings 8x AF 0x AA)

Tks
OH

 

[Drako]

The 7800 does not perform well using 8x AA. 4x AA works great though.

AA Comparison

 

[Lazlo Panaflex]

How bizarre...it was fubared even with an SLI setup! Indeed, looks like 4x is the sweet spot. Thanks for the link, Drako!

OH