I worked in engineering for an electric utility for 35 years. Foam on the upper side of an attic will keep the attic cooler, but won't affect the rest of the house much provided there is good attic ventilation and attic floor insulation to R-30 or better. Cellulose insulation is the way to go in walls and attic. FG batts, not so much. They are only useful IMO where cellulose won't stay put, like in spots where wind might intrude, like blocking off soffits from cellulose, and under floors.
