Sorry downwardspiral, the SRT-6's don't have 330 crank hp. That was false advertizing on the part of DaimlerChrysler. They actually sport 350 (or 349 depending on who you ask). The theory is that DaimlerChrysler didn't want to appear to be selling SLK 32 AMG level performance for cheap.

You are right in one regard, the limited is lighter than the SRt by about 180 lbs. So if a limited had the same hp as an SRT, the limited would be faster.

Keep in mind that the SRT-6's that you're seeing running 12.8's and lower aren't stock. The fastest recorded stock SRT-6 run was by Rob @ NeedWings at 13.044.