Most of the students from China are good students with decent grades and the most common reason why a student wants to repeat a grade is because of poor English skills which impedes the progression. Depending on the student's academic records, it may not necessarily mean it will be easier to repeat a grade rather than to ascend a grade. If your child's academic background is solid, I will not agree it's better to try 8 to 8 and if not successful, try 9 to 9. On the contrary, your child should try to ascend a grade and if somehow the result is not as you expected, i.e. rejection or waitlist, then you try to repeat the grade.
Repeating the grade obviously may result in negative psychological effects on your child (as no one likes to repeat a grade) but if your child is young for his age relative to the same class, it may not be a bad decision to repeat especially if your child needs the additional year to improve English.