It depends on the test. Below are for the tests that I have in front of me.
GR9677 is 80% with a raw score around 44-45
GR9277 and GR8677 are both 80% with a raw score of 55
I don't have the GR0177 in front of me at the moment but I imagine you can download it from ETS and see what the score is.
I think this applies to all test takers. I am pretty sure that you would need a lot less to be in the top 80% of american undergraduate students who take the test.
Keep in mind that the raw score is the number you get right minus i believe 1/4 point for every one you get wrong.
Man, you sure are thinking big shooting for 80%!