Fuji Track / Fuji Track Pro / Fuji Track Classic

it seems perfect for going downhill, i can go fast but i feel in control. the uphills are ok as long as they're not too steep! i'm sure this topic has been well covered on here, but how much difference would it make to go with a 16 or 17t cog?

The key's in the name. The gear's presumably as such because it's being set up/sold as a track bike ;o)
I expect most on here would opt for 16-19t for the road, and it does make quite a difference!