I passed the RAF medical a few years ago and I am almost 6'4".
They did comment that I might lose my kneecaps on ejection but they still put me through.
It's not just a straight matter of height but rather leg length and sitting height. That is, if you are tall, as long as you are slightly longer in the body rather than the legs, you should pass the RAF medical (on hieght grounds) and your knee caps should remain intact in the event of an ejection.