Being 6'5" tall myself, I find that even stuff marked as XL usually means it fits a sumo better than it does me. It might be long enough, but the crotch hangs near down to my knees, like Dick Van Dyke dancing with the penguins in Mary Poppins or something.
Truly tall sizes ought to fit better than that I would think.
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The ultimate result of shielding men from the effects of folly is to fill the world with fools.
-- Herbert Spencer, English Philosopher (1820-1903)