Your gearing isn't holding you back so much as air is holding you back - the faster you move through the air, the harder it is to move through the air.
For example, even though there's the same 3 mph increase, the difference in power required for 14 vs 17 mph isn't a heck of a lot, but the difference between 22 vs 25 mph is significant. I mention this because, all other things equal, simply going to taller gearing isn't going to make you faster - the power requirements at a given speed are (more or less) the same regardless of gearing, but the gearing gives you freedom to find an optimal cadence for your effort.
With your 50/14, you're looking at ~90 rpm for your 25mph effort - that shouldn't be spinning-out; for a lot of people, that's an average cadence.