As the experts have explained to me, there are basically three CX tread types
Rhino (Dugast, Clement PDX is basically same tread)
Grifo (Challenge, Clement MXP, FMB
File tread
Most people would say if you have two sets, get a Grifo set and a Rhino.
I run Challenge Grifo and Limus, I have some Clement PDX clinchers but don't race them. If I got another set of tires it would a tossup, file tread or rhino tread.
This having been a pretty dry year, I think file treads would have been nice to have in the arsenal. I also don't know what the best tire is for loose, dry gravel or dust. Maybe it is a file tread, in which case this would be a great September race tire for OR.