Zeeper and Caocao convinced me (actually Caocao - Zeeper probably still won't get it, but Caocao's an engineer so he will) to run some numbers. I took BigFatHorse's database from here:
and plotted the mpg's out. Zeeper's been talking about all the CVT's that get really good mpg way over on the right, so here's what he's talking about.
However, you can see that there are CVT's to the left as well (further actually) - that's because there are 140 drivers in the database with CVT's and only 38 with 5MT's. If you kind of step back (well, or sit back) and look at the big picture, you can see the 5MT's, despite that enthusiasts generally prefer manual transmissions, get better mpg with the Impreza. The average for this, the big dataset, is 27.7 mpg for the 5MT and 27.1 for the CVT's.