I have about three years experience with CC. My daughter in middle school is on the "accelerated" track which is traditional Algebra, Geometry, Algebra 2, etc. My younger child, in elementary school, is using CC math. He won't be allowed to switch into traditional math until 7th grade Algebra even if he is a child prodigy (he's not). The district won't allow it. The lower level kids stay in CC math throughout middle school and high school and will take the corresponding PARCC test. The gifted kids will take traditional math and the PARCC test to go along with that track. It is my experience that CC is math is a lower level math. It isn't more rigorous. It's just more confusing. It's supposed to teach at a deeper level, which is just too slow for gifted kids.
What makes CC different and confusing is the new methods the standards prescribe. For example, fractions are taught using a number line instead of a pie chart and multiplication is taught using the breakdown method. To pass a CC type standardized test would require some test preparation. The PARCC test also requires the student to type answers in complete sentences and to think about the answers in a different way. I think it's trickery and too confusing for elementary aged children. It's not an accurate measure of math skills, writing maybe, but not math.
I would try to avoid it if possible. The SAT will be CC aligned in 2016, but the ACT will not be.
I hope this is helpful.
