Mate, fire up this applet: Rabbit
(stolen shamelessly from the Gearing Primer at the top of this sub-forum) and get some figures to work from. With your gearing, you should be cruising at something over 20 mph. I say 'should be' based on a cadence of 90 being a pretty useful standard cadence, even for fat old phart's like me. If you're not cruising at 20mph or greater now, yes, you need to be spinning faster.
The thing about fixed gear is that YOU make the changes in the speed of your legs. Because the real world rarely lets us ride as we wish, this means that sometimes you will be pedalling slower than is desirable (and that places a lot of pressure on knees and muscles) and at other times you will be pedalling frantically. The thing about riding fixed is that you need to pedalling skills to be able to handle those high revs and quite frankly, if you can't pedal at 120, you are not going to be able to ride undulating terrain on a fixed gear bike - with your gears, that's greater than 26mph.
Now don't get excited and try to bluff yourself with inflated speeds, there's a world of difference between hitting a speed and holding it. Quite frankly, it's your legs that are going to be complaining long after other people have stopped admiring your gearing. Gear up too much, and you will stuff up your knees and legs - young blokes can do that for a long longer than us old wombats but it catches up to all of us in the end.
I wouldn't up my gearing unless I regularly found myself pulling a cadence of greater than 100 on the flats. Down hill, it's a non-issue, just teach yourself to spin faster and believe me, the thrill of spinning smoothly at 140 is pretty awsome (it feels like you're part of a turbine if you get it right).
You don't use brakes. Every time you up the gearing, you make it harder to control your speed and you increase your stopping distances. Make sure you have a ton of stopping clearance BEFORE increasing your gearing.
The real world is rarely straight, flat and devoid of things to slow you down. Increase your gearing and you will make accelerating harder and once again, it's them leg thingies that will complain first, not the bike.
Real world urban warfare usually means that you don't get to pull your preferred cruising speed for long and that you spend more time slowing down and accelerating than anything else. Increasing your gearing will make that harder and you will probably find that you don't get many opportunities to use the bigger gear.
Then there are the issues discussed above.
all of that is bulldust. Just go out and buy yourself a 16 tooth cog, spin it on the back and try it. If it's still on there in a month's time, you made the right choice. If the 17 is back on, well you won't lie awake at night wondering about whether you want the higher gear.