Alright, after quite a while of tampering with the design, I think I have a winner.
Introducing the U.S.S. Vainglory, as it goes to Proxima Centari B and back in 27 years, and has a one way travel time of 13 years.
The main power source is magic a quatum singularity reactor with a magnetic nozzle attached, combined with more magic Mach Effect thrusters as afterburners. For the record, although the STL systems in KSPIE are pretty balanced, these parts are crazy good, even more so than antimatter reactors, so naturally, I had to exploit them for profit maximum speed.
Proof (Warning: Long):