For speed, the Japanese style hand saws work nicely.

Our ancestors would often times not have used the one handed panel saws for this purpose, instead they would have used either the large 2 man crosscut (or a one man version) or a frame saw. Both of these have benefits which allow you to cut through a timber in a hurry, especially the fact that both of these types of saws in the past tended to cut on both the push and the pull stroke.

A good frame saw, or buck saw, really can't be beat. It would certainly be worth looking into. And if you have a helper, using a good old 2 man crosscut in good condition is going to be the fastest way.

What's most important on these saws is: how sharp the teeth are (dull teeth obviously cut poorly) the set on the teeth (too narrow, you bind up a lot, too wide and you're not gonna cut cleanly) And the tooth pattern (different patters for different wood)

The frame saws for this purpose have teeth in a crosscut-style pattern, rather than the triangular teeth of the panel saw.