My friend built a pole shed, would hold about 4 vehicles I forget the exact size, 12' walls. Up here in Minnesota, it has 8' spacing on the poles & on the trusses. It was designed & built by a pretty good company that does it for a living. And we have about as much snowload as it gets here in MN, as well as wind load - he's on the Buffalo Ridge.
So, wide spacing can be done. It has pretty good purlins of course.
--->Paul