I'm with Krusty, I'd start by pulling the AA down. I might even try dropping max texture size down one.
Might experiment even with lower screen resolution. As all those are easy to change and reset back to where you had them.
Also try turning the local water reflections off, see if that helps.
Also I wasn't following if you had a sound card vs onboard sound or USB headset, either of which will rob CPU cycles when you need them most.