anyone know a formula for rearend gears

Does anyone know the formula to calculate for what gears to use in the rearend.I cant go back to the track until spring but heres a little back ground I have 4.30 gears Auto transmission with a 4000 stall and 28" tall tires. My engine is set up to shift at 7000 RPM.

Use your flywheel HP to estimate your trap speed. Gear the car to put you a couple 100rpm below redline at the finish line. You need to figure in convertor slip and tire growth.

That's a 600-shot your spraying?

I am going to be spraying 400 for now