would would be the best bang for the buck bbk shorties or xcal2. current mods are 3.73 gears, cai, x pipe, steeda under drive pullies, and weld in flows
If you look at the power curve on the BBK shorties you lose power low in the band to gain power hight in the band. probably not much there in the ET department. if going to the trouble to do headers I would not pick shorties. I would consdier midlenghts if there were ground clearance issues.
the xcal 2 is more hp most likely and easier to install so to speak as there is not install.
now longtubes are going to give you more power than the turner most likely.
I got the FMS shorties, and the car does breathe a bit better, but if you want headers definately go with longtubes, i am regreting it now. But for now, go with the xcal2. I am getting one soon also.