[SPF1061]

I have been following this thread and have found very little info/suggestions regarding the original question. I would like to steer it back in that direction for a moment. I own a Roush 427R with an AED HO-Modified 750 cfm carb that is dialed in. I am running 4" stainless specialties mufflers. I tried the larger diameter SPF headers, but the torque lost down low more than offset the the free-er breathing I got at the very top end. Actually lost hp and a couple of tenths off et. The car runs well with no issues. (11:30-11:50 sets depending on weather). The issue is simply that I have become accustomed to this much power and want more. What would the informed reader suggest to take this engine to the next level without destroying it's street manners. I do not want to go to a solid cam. Any suggestions?