Well, this is also anecdotal, but DD and DS both have similar-color eyes (light brown/hazel). DD is _very_ pain-sensitive, and DS is almost under-sensitive to pain. So in our case, it doesn't seem related at all to eye color.
Another anecdote - when DS was 2 yrs old, he had a surgery on his eye. While in the recovery room the surgeon came out and said that since DS has red hair he may feel the pain more, and gave him a shot of morphine. Well he never complained about any pain (he usually doesn't unless it's bad), but the morphine made him vomit continually. We had a miserable time until the nurse gave him a shot of Gravol.
(I've no idea of their processing speeds, but I suspect DS's would be low).
