The Gunnar Sport would make a great fast commuter and could probably be built for about $2K, and much less if moving parts from another frame or building from used/discount parts. Soma Smoothie or ES could be built for about $500 less.
I've commuted on many different bikes over the years, and the biggest factors affecting speed were the tires and the amount of loads/gear I was carrying (not including external factors such as wind, rain, traffic, red lights, etc.). My fastest regular commuter was probably my Eddy Merckx Corsa 01, but it barely had room for fenders with 25 mm tires. My De Bernardi was even faster when I briefly had it rigged up as a single speed, but that was brutal on my knees and did not last very long. Currently, my fastest commuter is a Waterford RST-22 sport touring bike with no fenders and 25 mm tires. My other commuters have larger tires, fenders and rear racks so they are heavier with more rolling resistance.