Low-latency read of UDP port

Question

I am reading a single data item from a UDP port. It's essential that this read be the lowest latency possible. At present I'm reading via the boost::asio library's async_receive_from method. Does anyone know the kind of latency I will experience between the packet arriving at the network card, and the callback method being invoked in my user code?

Boost is a very good library, but quite generic, is there a lower latency alternative?

All opinions on writing low-latency UDP network programs are very welcome.

EDIT: Another question, is there a relatively feasible way to estimate the latency that I'm experiencing between NIC and user mode?