Standard or extended maths in MYP for grade 9? His teacher says either would be fine

Grade 8, IB school, and our son has to choose between standard and extended maths for next year. His marks put him somewhere in the middle. He is not passionate about maths, but he is not weak either. The teacher's view is that he could manage either. Extended keeps more options open for the Diploma years, and we don't know yet what he will want at 16. Standard would leave him more time for the subjects he enjoys, and he is already stretched with design and language assignments. I can't settle it. Choosing extended to keep doors open feels sensible, but it also means a year or two of him grinding through something he may drop anyway. If your child faced this choice, which way did you go, and did it matter later?