Well, I'm also 6'6" and passed all ab-initio tests in one of largest nordic flag carrier, now finishing my studies. Have 0 problem for fitting in Piper, Cessna 172 or 152, and dont have any leg-cramps on what-so-ever even in 3h crosscountry flights. Only problem, that I have had since now is rare headache, when my stupid head hits upper wing of a cessna. But this is now rare happening ( in the beggining, that happend about once a month)...
If you are still worried, go and ask for the school where you want to go, or in airline, in which you intend to apply. IIRC, that BA have/has height restriction and it was about 6'3", but in the application was memo which stated that if the applicant doest meet the height restriction, he/she must demonstrate ability to fit in .. or something similar.