Stock 340 manifolds value

Question is, on a motor with 325 horsepower or less, what is the gain on the 400 dollar 340 manifolds over the log style I have on my motor? If it's only about 10 hp, then I wouldn't pay 400 bucks for 10 hp. Unless it's a resto, IS there a hp justification for the money?? My style are easy to find and sometimes can be next to free...