I would try and allow the conversation to flow naturally.

If they have wikipedia pages, it is perfectly acceptable to mention anything on that page (well leave personal/family stuff out - "So is it true you and your wife divorced in 1993 and then re-married in 1998? Wow!" that will not get you far). Anything that you could've read in the paper, you know, I think you can mention too - "I read an article about your new initiative to do x. I thought it was interesting but had a question or two about the concept, would you mind talking about it?"

A lunch meeting is kind of hard because sometimes people don't want to talk about work at lunch, it's your mid-day break, so I would see how the mood and intent is feeling.

I would just not go overboard. Don't show your hand. You know their entire history, that's like let's say 5 cards (we're playing poker). If you're going to do anything show one card, one fact, one question, whatever. See how it goes. DON'T rush in there with a million questions and clearly displaying "Hahaha I know everything about you!"

Once I met the wife of a poet and I said "Oh yes you! I stalked you on Facebook!" I wasn't interested in the poet; he wasn't cute or anything, I just meant I'd seen him posting about her because they hang out a lot and I was mildly curious. I thought it would be funny. She clearly thought I was weird. So...don't make it obvious.

I mean, important people in my organization, I'm at least supposed to have an awareness of their work history - how long they've been in the company, where they were before this, etc. First thing higher-ups do is tell you a history of how they got to where they are basically, read off a resume. So I don't think it's TOO unusual.