I would say that 6'6" is abnormal tall. I'm 6'4" and I think of someone my height as being at the uppermost limit of normal, meaning we can get clothes that fit at most clothing stores. Once you get past that then it gets difficult. You'll come across someone my height almost every day, but a guy 6'5"+ not as frequently.
6.6 is not abnormal, but it is unusual.
According to this chart: http://www.allcountries.org/uscensus/230_cumulative_percent_distribution_of_population_by.html .
80% males are UNDER 6 ft tall.
12% are 6-1 or taller.
7% are 6-2 or taller.
4% are 6-3 or taller.
2% are 6-4 or taller.
I once read a study that said when men go over 6-5 in height, the social advantages of being tall reverse and height starts to become a disadvantage.
As far as golf goes, the few advantages (being able to more power) are quickly outweighed by the disadvantages.
Adding an inch to the club length (1) causes the swing weight to shoot through the roof, (2) makes the shaft more flexible, and (3) makes it more difficult to hit the ball in the center of the head.