I like to go with Larry David's advice with skipping the small talk and going straight to medium or large talk. I like to open with "so how's your marriage?" Just get right into it.
So, I've had people lay these kinds of questions on me. Or even during a job interview (!). And normally, I'm down for the deep shit at the drop of a hat. But the problem is when complete strangers ask me these questions. It's hard to gauge when a conversation about the last time I did MDMA (and why) is appropriate. Do I really want to talk about the nasty shit I did in Iraq with complete strangers, even though that's the most honest and direct answer to their hail mary of a question? Even something like "So how are you really doing?" can be challenging to answer to a stranger. I guess really I question your desire (or ability) to handle the answers.
It hugely depends on how it's asked. If you ask it in a really awkward dead pan kind of way it's going to fall flat. If you do it in an almost "indulge me" kind of banterish irony, most people get that and will string along for a bit. The funny ones will go along and end it with something like "wow, really took me for a ride there" and switch it back on you.
How does that work for you? I figure it's a good filter - 80% of people think you're a whackball and run away, 20% stay and have interesting conversations.
Do you really have to go for such a personal and emotionally charged topic to start "big talk"? Obviously anything actually important is likely to be somewhat less comfortable, but there are still degrees.
I think most people are going to be much more comfortable talking about art, philosophy or politics than about their personal life, particularly with a stranger.