th400 or 700r4
A 700r4 and 4L60E have basically the same internals. (A stock 4L60E, especially later model 4L65E and 4L70E are stronger than a stock 700r4).
A very well built 4L60E (true for 700R4 too) costs $4000+, and still will not support even 800HP for very long.
For any car at that power level and street driven I would suggest a 4L80E as a mildly built one can handle that power level.








