I would have to agree with Rick and the others ... Stick with a Porsche for the refined reide quality and handling. These cars just won't win on the drag strip BUT take them onto a tight, twisty road and you will certainly have an advantage.
As far as the upgrades go: I would move into a 997, 996, or Cayman S (probably in that order). With the 911 the handling is different but you might have the increased HP you are looking for. The Cayman might be a good middle road with the upgraded power while still retaining the mid-engine layout we enjoy so much right now.
Best of luck with your decision!