I run a 46/17 with a 700x38 for 74.6 gear inches & about 90rpm@19mph. Works good for the local conditions. Spin out at 160rpm for some fast downs. Kick out 45 rpm & a pile-o-watts for the steepest hill I'm able to climb near my house. (But can still do it.)

Gearing is very individual based on locality & individual fitness. I'm not sure crowd sourcing a bunch of data points clustering around some average of around 70 gear inches really is going to mean much other than "most single-speed riders ride at or about 70 gear inches."