2x4 or 2x6 for insulation
We're planning to build our 30 year house here in NE Ohio. 2 story, around 2500 sf. Our builder said he builds using 2x4 exterior walls. I was thinking of 2x6. My primary goal is to build an energy efficient house. What is more cost effective, using (A) 2x4 with spray foam insulation, (B) 2x4 with batts and exterior sheathing, or (C) 2x6 with Pink Panther insulation?