Guess playstyles are different then ^^
I just like being able to carry games hard and the best way for that is just to get a Triforce early to get insanely strong ganks, with your build I'd guess you farm more and are more a teamfight guy. Correct me if I'm wrong ofcourse, but that's what I get from how you explain your build
Just tried Wit's End in a game again, enemies were 3 AP champions, in that case it's ofcourse a very good choice but I think when you meet a team where the enemies have only 1 AP Wit's End isn't a good choice. With 2 AP's on enemy team it depends I guess.
I still like Sheen early better then Wit's End, oh well ^^