Re: spray foam insulation
Being that you are a contractor you are familair of the perm. value of materials.
If you are using a closed cell foam this material has a low perm value for air and moisture penetration.
Combined with the low perm. value and it's high R value closed cell foam works toward greatly reducing the warm and cool zones from meeting. As well the spray foam will seal voids in the structure preventing air leakage which is more difficult to do with batt insulation.
As with any insulation all areas of air leakage need to be addressed not only the stud bays.