I have some fast track LK's on my epic, and I like them a lot. They roll really fast, and grip surprisingly well. The trick with them is to run them at slighly lower pressure than you think you should. I run mine at 33 rear, 27 front, and I'm almost 190 pounds. They don't really start to have problems until you're below 30 psi in the rear, then it starts to wallow.
If you do decided to go for a bit more aggro setup, I'd keep the rear tire and just replace the front with something knobbier. The the fast rolling nature of the fast track is worth it, imo.