If I were you, I'd keep the 46t chainring and go with a 17t fixed cog. This will give you about 73 gear inches and 17 skid patches (if you are into that sort of thing).

I run 48/18 on my Messenger and that has been fine for the rolling terrain around here. The downside to this gearing is only having 3 skid patches.

The difference between the fixed/freewheel sides doesn't matter because you'll be having so much riding fixed you'll never flip the wheel back to the freewheel side anyway.