I feel somewhat ashamed by the briefness of this reply following simons discussion of the topic, but for what its worth my hack bike for getting around town is an old mtb frame, slicked up, fixed and running 49x16, and i cant say ive ever had any bother with it.
I suppose in terms of developing "suplese" (pardon my french spelling) a lighter gear would be preferable for spinning, but for general cruising about town i have found this nice and quick on the flats and manageable both uphill and down.
Enjoy it, whatever gear you choose!