307 low end torque loss from dual exhaust?

[chevyc1068]

Would a 307 engine lose any low end torque (or high end or any where) from converting the stock single 2inch? system to a dual 2.25 system with headers? If it does where and how much? Or would it gain any. I've heard of the supposed power gains from headers and a more free flowing exhaust system. If so how much gain are we talking about.