Hi,
I've been scratching my head on this for quite a while.

When I turn on the A/C, the engine seems to dip or fluctuate a lot more than I'd really expect from an engine with this much power. It will be at nicely at 700 and drop as low as 400 briefly before recovering. It seems to do this whether in drive or park. Is this normal for other owners? I've tried to find vacuum leaks, etc., and haven't found anything. It drives fine, so far as I can tell.

One thought I've had is supposing that the supercharger actuator is marginal -- and toggles on and off the boost. It's a little suspicious to me that I haven't seen people posting about this part failing -- I can't see why it wouldn't at least occasionally happen to people. Maybe the symptom is, like this, and subtle enough to ignore.

Any thoughts? (Or is this just normal?)

Could it be the AC pump that is causing the issue. When engaged it is initially sticking but due to the power of the engine it is freed up and the revs resume. Just a thought.