How much it will gain to update a temporay table insteand of a permenent table

There is big table(only store temporary data) to be updated often in the same procedure. I want to persuade the app team to change the table into global temporay table. But I am not sure how much it will gain for this change. Update on temporary table will not generate redo, but it will create undo, so roughly I think it will only create half the redo as the normal table. But for the test I did, the redo size varied a lot and I am not sure we can get a perceivable improvement.

Thanks,
Qihua

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