To me the yard turnouts should be smaller than the mainline turnouts. I would use #5 as a minimum in a freight yard and #6 in a passenger yard. My longest freight cars are 65' and my passenger cars are 80'.
I started this layout with #7 turnouts on the mainline and have built new trackage with #10's since they were introduced. I wish all of the mainline turnouts were #10's. I plan to replace any failures with #10's were possible.
Waltzing Creek & Western Railroad