A well built stock Dual Fed 4L80E with Jakes PR spring will handle 500hp easily......
You really don't need the Sonnax Overrun kit.....If you're going to beat on it, Use D3....This brings on the Overruns & helps support the O/D Roller Clutch. The Sonnax Overrun kit is more suited to loaded/overloaded "Company" trucks that get thrashed by employees.
Deleting the 3rd & 4th Accumulators & Housing is recommended on most all performance builds.