For boning out deer/antelope .?
4.5" to 6"
The traditional boners from French and German factories are 5". What I grew up with, like the Buck 118 at 4.5", the Randall 10-5" made the DR and Forschner seem WAY too flexy and quick to dull.
When I found Makers who had realized this and were making KICK-ASS replacements I was sold...