Stock headers are shorty headers.

Not much difference. Any gains by aftermarket shorty headers is negligible at best.
If your looking for an honest performance improvement just ditch the whole exhaust and go with long tubes and an off road mid pipe. No other bolt on short of nitrous or FI will see a better gain.
Long tubes, offroad mid pipe, cam and a gear will wake the car up. Your only teasing yourself with shorty headers vs the stock exhaust.

Hurst