I use 2.5k too for optimal mileage.
I also am running the SPT, my mileage actually went up as a result of the exhaust, again assuming I stay out of heavy boosting.
I envy the roads you get to drive. Unless I go into the mountains everything is pretty much perfectly straight here. Sounds like I may need to upgrade to a Thule rack, the Subaru one is VERY noisy.