Eagle,
Initially, I'd shift at the shift light. This light comes on at 5700 rpm, but is behind the actual engine speed, meaning you will be shifting about 5800 - 6000 depending upon your reaction time, anticipation and timing in general. This is about right but will vary a little bit with each car, air temperature, humidity, track prep, etc.
The rev limiter in my car was preset at 6200. I had WCV reset it to 6400 after I added headers, exhaust and intake mods.
I have a GTS too and it is a very different animal in stock form. Very "torquey" but runs out of breath at about 54-5500. The SRT-10 wants to spin higher.
This car is very difficult to launch compared to other cars I have driven and a bit slow to shift. Tires break loose a high speeds and the stock diff isn't very friendly at the drags. Like you, I had dragged a bunch, but still haven't mastered this car, now due largely to mods and power level. I intend to continue to practice every chance I get ... and so should you.
Good luck,
Dan