Low 7950 performance in Serious Sam 2?

I get 8300 in 3DMark06 with

Core 2 E6400 @ 400x8 (3200MHz)
2GB PC6400
Gigabyte 7950GX2, stock clocks

Games like BF2 and HL2 fly over 60fps at 1920x1200 with 4xSSAA and 16xHQAF. But in Serious Sam 2, I don't do nearly that well. If I play the second demo from the main menu, I get 20-30fps. Same goes for the first level of the game, where I'm lucky to get 50fps.

Obviously I'm playing at ultra high settings, so I probably shouldn't complain, but the website benchmarks I've seen of SS2 all indicate that it performs on the level of HL2, especially on a machine like mine.

Anyone have suggestions? Again, not a serious issue, just curious what kind of performance you all get in this game at high settings.

Does the sound stutter at all? I tried the SS2 game demo and I too had pretty bad performance.

No the sound is fine using X-Fi.