As a general rule, I use the largest gear ratio that I can and still maintain a decent cadence on the steepest hills on my ride. I find that I am fastest overall when riding 49x16 than, so thats what I ride. Lower ratios slow me down on the downhills and flats. I've tried higher ratios but anything above 49x16 and my cadence ends up being slower than I'd like most of the time, and I have a harder time keeping my momentum up the steeper hiils or in headwinds. Higher ratios are great for sprinting though.

It never hurts to experiment. If I were you, I'd try 48x16. You may at first feel like its straining your legs, but keep hammering and give it some time. You may find that it makes you faster. At that point, if you still feel like you can go higher, try a 15t and so on. At some point you will discover that you've gone too high and need to back off a bit.

I change the gear ratios on all my bikes a small amount throughout the year. In the winter I'm less interested in speed, so gear lower and work on my spin. Then in the summer, put the bigger ratios on and focus more on going fast and using my strength.