I'd go with "pretty tight"
I'm don't know a single store with a torque wrench. Hell my mechanic doesn't even use one unless he's got the block open.
All that said, a quick google tells me that 4Nm is the number thrown around a lot, although thats for screws straight into the core
Disclaimer: Following internet advice about bindings will cause your skis to catch fire, your nose to fall off and your cat (if you have one) to piss in your boots. So don't do it.