Is there any client lag which is intermittent, caused by an antialiasing mode which is maxed out for my machine?

AA mode off, Plugins disabled, no lag.
6x AA mode on, Plugins disabled, intermittent lag.
6x AA mode on, Plugins enabled, intermittent lag.
AA mode off, Plugins enabled, no lag.
I know I seemed to have solved my own problem, but has anyone else ever experienced this?

6x AA mode, MacBook Pro (late 2006).

Intermittent lag where like you at playing an then the who game freezes on a frame for like a second, then continues? I get that in some circumstances. Your post makes me wan to try those without aa

Aliasing should not cause lag - It might slow the overall frame rate tho.

Well that's what I thought. An overall fps decrease.
But this is happening just like Espionage describes.

UPDATE: just happened without AA mode on.. perhaps it's another graphic setting.
Maybe when the field of view runs over something large, it has to process it?
All of my other settings are maxed out, I'll try reducing those and see what happens.

AA drastically increases your frame buffer, which has a non-trivial impact on video ram usage. If you're close to borderline with your video-ram usage already, then adding AA will potentially induce texture thrashing in some situations, which is definitely undesirable.

Conversely, AA also can have a big impact on fillrate, so if you run into a situation with a lot of overdraw, your fillerate may drop to a point where your framerate suddenly declines.

Either situation is possible, is entirely based on what's in the scene at the given moment, and basically just means you're asking too much of your hardware.