4.30! Wow. With my 3.73s and my drag radials, which are a little smaller and take my ratio to about a 3.9 it seems like I am running out of motor by the end of the track. And I have put down a 1.7 60' so I am sure that you have a lot more in it than you are pulling out of it right now.
It's very smart to take it to a dyno to do your tuning, and I also applaud that you are running conservative. I have always been of the opinion that I'll trade a couple of tenths to get to DRIVE the car home.
Past the nitrous and the gears the two biggest things that impacted my time was the stall converter (As mentioned by Burbank) and a progressive controller for the nitrous. The progressive keeps that huge hit from nailing the motor, and makes the whole thing feel more like boost. It also helped with my traction.
You are on the right path, and I commend your choices and plans. Keep us posted, you have 12s in your future!