I ride 75.6GI in a very hilly town, and it feels just about perfect. I have to mash the pedals on quite a few inclines, but I also have enough top end that I don't coast too much (I ride SS, not fixed). I plan on upgrading to lighter wheels and tires in the future, and I'll probably swap my 16T for a 15T, which would give me 80.6GI.

I think one's preference has a lot to do with where they ride (flat areas vs hilly) and overall leg strength.