I just feel like if you're going to ride a fixed gear, why not run the highest ratio you can safely slow down on as well the highest you can handle? It only makes you stronger, which logically, will make you faster. At the very least, you'll be able to run higher gearings after a while and then just spin at a comfortable cadence while bombing down hills going ludicrous speed. And your bike will look cooler.
In my experience, riding 75gi for a long time did nothing. Aside from that, riding fixed never felt quite right until I started gearing down and spent a long time on 48x18/19. I'm sure in a totally flat area I would opt for a higher gear, but the terrain changes a lot here and hanging under 70gi feels the most versatile for me. When I flip the flop I am set with 73gi. I ride that around every once in a while for kicks and to change it up a bit ,again, it doesn't feel "right".
I do climb a lot in the Hollywood hills and have gone out with guys riding larger gears. Looks cool, wish I could, doesnt happen.