Must say went fL100 t'other week with Mr Horgy . passing 9000 I started to get a banging headache and had difficulty focusing properly on instruments .My breathing was also affected . Lcukily the much younger man was flying and was unaffected , bt it certainly gave me what I think is vaulabe information , I now know my no oxy limits . I will be going no higher than 85 when Im PIC . Intersting experience