I think length is less of a problem than girth. With a new female partner I have to go carefully the first time with pussy fucking until I know how deep she can take me without feeling pain. (My current girlfriend has a deep pussy,) And when it comes to a long cock, you should be able to go balls deep anally if you angle yourself the right way. I have a buddy who goes crazy when I get past that second barrier — he says it's like every pleasure nerve in his body has been turned on.
A cock that's too thick is another matter. Trying to get your mouth around beer-can girth isn't much fun for anyone. Stretching a pussy or ass a bit is fun for both the top and bottom, but not if there's a danger of ripping things apart. I'm glad I have a big cock, but especially glad it's not too thick. What's good enough for Brent Everett is good enough for me