TOEFL Equivalency Table - TOEIC, TOEFL, IELTS Score Comparison Chart
A student who took three exams, TOEFL computer, TOEFL internet and FCE at the same time, and gained 153-180 on the first would be expected to gain 53-64 on the second and to pass the third. This would depend on a number of external factors, and assumes that the student has been properly prepared for each exam.
It's not really a question of one exam being easier or more difficult than another.
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