Here is a stock BRZ compared with mine on 91 pump gas.
Mods are Nameless Performance EL header, Nameless Performance 3" downpipe, (oem midpipe), Greddy SP Elite axleback, and HKS drop in filter. Tuned with Ecutek. The Nameless header turned the torque dip into a torque hill. Love it. Eventually got it retuned on E85 (same mods) and here's what that looks like. Green line is previous pump gas tune.
I'm probably leaving some power on the table with the stock midpipe, but I had a 3" midpipe before and the car sounded terrible. Way too raspy. Maybe I'll do the Nameless 2.5" midpipe eventually. I've been driving on that tune for over 2yrs now and the car still feels amazing. A small turbo is tempting but the car is really fun to drive NA. Hope to do a intake manifold upgrade and maybe cams in the future. If I can squeeze an extra 15-20hp through most of the power curve that would be great.