Heads, how much gain?

So what I hear people saying is that if I were to buy some Eddy aluminum heads, I should pay some extra money to have some porting work done even if I am not going to race. I have been thinking about buying a pair.
I think Eddys may be the best value. Especially for a performance street build. If you have a good and trusted head machinist/builder? I would buy bare. And let the shop buy the valves and assemblies. They may already have a set of stainless valves (As an example) That may work much better with their port job. It also gives them more options than just dropping off Edelbrock's parts and assembly. Im not suggesting just giving the shop free reign on decisions? But to allow some flexibility. JMO of course.