I had a spot of bother with a slipping Thomson post on an old frame, duly sorted with a dap of carbon assembly paste and a nice wide Salsa bolt up seat clamp. This comination worked a treat on my next frame (853 Inbred). I've just moved onto a new 853 Sirius frame and transplanted the Thomson. In the process I've treated myself to a nice new QR Salsa clamp. The problem is that despite the post seeming to be a much better fit in the new frame I've been experiencing a bit of slippage again, despite the Salsa clamp and assembly paste.
I'm okay about nipping things up a bit tighter until the issue is resolved but I don't want to overdo things. Presumably you want crack a seattube of crush a post (although hopefully the clamp would go first). Online torque values for seat clamps seem to vary wildly up to around 15nm which is well over where I'm at. How high can I go with a steel frame and aluminium post?
I'd assume its all frame/manufacturer specific. I recently bought torque wrench to avoid exceeding the 10nM limit on my Whyte. Slip has stopped.