Fastest ship is currently an Excelsior retrofit with Borg engine. It can Transwarp to almost all sector blocks, and when it's not transwarping it's traveling at over warp factor 20 with the subtranswarp engine.
While Driver Coil will help you go faster than the basic Warp 14 of the Borg Engine.
It is a next to useless skill, it does mean your full impulse doesn't drain as much power but any competitive build skips it for something that actually helps you. Your better off asking for the Buff in Sector space.