Being 6'4" tall I really sympathise with the OP and many of the tall respondents here. Fortunately for me, advancing years and wealth mean that I no longer need to sit in Y.... oh..... hang on a minute, yes I do! Since those idiots at BA revenue management crunched the CE seats to the same pitch as Y, my only BA short haul choice now is to sit in the exit row. Since BA made this move I have experimented with a wide range of the competition, including those who fly from UK regional airports. Unless and until BA offer a legroom seat in CE then I will continue this trend.

As for the brace position, I was taught in helicopter escape that the head is a heavy object that can break your neck if it rattles around too much, so in a cramped seat and in a brace situation I would put my head against the seat in front of me and use my arms and hands (fingers unlinked ) to secure it. I would have my feet as far forwards as possible to prevent them from being flung forwards, because as others have said, I would need them to escape.