In addition to what's been said, this is a difficult question to answer because much of it depends on your ability to move around i.e. whether or not other planes are around you that limit your ability to move to less turbulent altitudes without conflicting with another a/c. A lot of routes may have no turbulence at one FL and considerable turbulence at another.

The flights to and from Japan all leave in waves so it's very crowded in the skies there. Hit turbulence and you generally can't move to get out of it because you're all stacked up and side by side.

[This message has been edited by letiole (edited 08-31-2003).]