I come from years of CS 1.6 play where the default _snd_mixahead is .1 (100ms), and I've always used _snd_mixahead .05 (50ms).
Quakelive has similar command "s_mixahead" and I'm surprised the default value is .14 (140ms!)
I figured I'd share with you guys, I was able to get down to .06 without sound stuttering (if you set it too low the sounds cut out)
If you're wondering what s_mixahead does exactly, it's the delay for all sound events ingame. So as an example if you are cornering against rocket, with lower mixahead, you'll hear his rocket fire event sooner :P
You're welcome ^_^