There is no necessary relationship between the two, and IELTS and TOEFL have no prescribed scores. Different countries, different schools, different degrees and different majors have different requirements. For example, IELTS is 5.5 for undergraduate students and 6.5 for master students.

If you get 425 points in CET-4 and prepare for one or two months, I think 5-5.5 is fine.

A score of 425 in CET-6 will probably get 6 points. 6.5 still need to review well.

I got about 450 points in CET-6, then I prepared IELTS for more than one month, with 6 points, and then I reviewed 6.5 for half a year.