I never won vs Emperor/Immortal with a wide empire that I built myself. It naturally becomes wide when I'm paving a domination victory, which comes way after I get most of my NW's.
I usually stall my empire at 3 cities until I finish Heroic Epic, Ironworks, National Treasury, National College.
Then I widen my empire to 5~7 depending on the state of the game and landscape. My friends who play with super wide empires ignore wonders entirely Q___Q (and then lose terribly to me in the late game)
Oxford and Hermitage gets the short end of the stick. I buy University/Opera House for every city depending on which one I need earlier (I can't afford both). Oxford for Astronomy ocean rush, Hermitage to finish some vital trees.