Definitely gear down. I got a Fuji Track Pro last year. It came stock with a 49x15 gear. Great for the track but way too big for the road. I got 45t chainring and 19t cog for spins around the neighborhood with a little undulation here and there. In a perfectly flat area, that 45x19 would probably be too small a gear, but it works here.

So to each his own, but I think most mortals with fixies on the street won't be well served with a 49t or 48t chainring no matter what size cog you rock. Depends on your area, but a 46t chainring should give you a good range of choices for spinning on your FG rides.