I am finishing a bonus room with a cathedral ceiling. The roof is made with 2x8s and I am wondering if I should build out the rafters with 2x2s so I can install R30C insulation that is 8 and 1/4 inch thick. Or should I just use R-19 6 1/4 inch thick? Is the extra R value worth the money and hassle? I live in CT with cold winters and hot summers.