They work in Canada because that is what we are told to run. I have no issues running on them so tell me that is what we run on in the US & I will do it as well without complaining.
It is likely easier to have less noise going to a R60 or similar tire but as others have pointed out go to a limited number of tires per event as well.
Why not have someone ask the tire companies what they are willing to do if the SCCA can mandate a spec tire? Would seem to make sense before any decisions were made what we can get from our supplier.