That’s a good strategy. If a junior (2017) has started studying SAT and expects a decent score, I would highly encourage taking the old SAT. There is one more, final chance on January 23.
If a junior hasn’t looked at the SAT yet or is getting not so good score now, I would say go for the ACT.
The March new SAT scores won’t be released until June (unlike old SAT getting scores back sooner.) No feedback till next two SATs are over. Then the next test is in October which might be the last possible test for some.