I don't understand the question about "scaling" one's score. You are told your percentile. There are conversion charts for translating the ACT to SAT or vice versa.
I don't see why you would get more flexibility just because the grading scale is different. Schools will want a similar level of performance regardless of which test is selected.
Ask potential colleges if they have a preference. Everyone I ever talked to said no. Since there is nothing wrong with expressing a preference if they have them, and in fact colleges used to do so and have chosen to move away from that, I see no reason to believe they are lying.
Most people applying to colleges submit the usual test results either because they and those colleges are in the geographic region where a particular test has historically been used OR folks are sheep and want to continue to do what has usually been done whether it is necessary or not. I imagine most kids submit SATs to NYU because it is in New York and people tell them that east coast schools "prefer" the SAT. What NYU itself tells people seems to make no difference. If they get ACT scores, they will just translate them into an SAT equivalent.
In other words, unless you want to go to the one place I know of that requires the SAT (Harvey Mudd), you should simply go with the test you do the best on.
I live in SAT country. My daughter only took the ACT and is attending Brown, even though most everyone applying there submits SAT scores. So many people around here thought she was doing something so incredibly risky. Really, riskier than submitting one's weaker testing to a very selective school?
This seems to come up so often on CC. I really wonder -- are school GCs clueless or what?