I've ridden 46/16, 46/17 and 42/17 and a geared bike on the same route many times, and from my experience I always got to my destination at approximately the same time. Speed depends on your output. Having the tallest gearing doesn't mean anything if you can't spin a comfortable cadence. This may seem counter-intuitive, but you should try 39/16, you will really feel the difference in comfort and perceived speed. Lower gears keep me motivated and don't tire me out as much for longer distances, sometimes resulting in higher average speeds by the end of the trip. Ultimately, it depends on your riding style; I hate mashing.