There is very little reason to submit both SAT and ACT scores to colleges, even if you are also submitting SAT II scores. As our blog article on this topic states, while in the past it was true that selective colleges preferred the SAT to the ACT, this hasn't been true for a long time. You are also correct that, percentile-wise, even an ACT score of 33 puts you in the 99th percentile, while an SAT score of 1470 puts you in the 97-98th percentiles.
The only reason you might want to consider doing otherwise is if A) you're submitting SAT II scores to the school anyway (since thanks to College Board's Score Reports policy, it won't cost any extra money to do so) AND B) you did significantly better, percentile-wise, on SAT Math compared to ACT Math or on SAT Evidence-Based Reading and Writing compared to ACT English and/or ACT Reading. For instance, let's say that somehow your composite score of 33 on the ACT breaks down into E36/M24/R36/S35, but that on the SAT you got 800 on the math and 670 on EBRW. In this case, you'd definitely want to also send your perfect SAT Math score.
As to avoiding having to submit SAT II scores by submitting your ACT scores, this ExpertHub answer elegantly explains the downside. Basically, the SAT subject tests can be a way of highlighting your skill and interest in a particular subject (for instance, Physics) that wouldn't be evident from your ACT score alone. This only applies if you do exceptionally (approximately 95th percentile and up) well on the test, however; there's little point to submitting a mediocre SAT II score and having that diminish the positive impact of your 99th percentile ACT score.