I've only checked it once, but somewhere in the low 20's in mixed driving. On the highway in 5th/D the car only turns 2k rpm @ 60.

For most cars, the automatic will cost you 1-2 mpg over a stick. The blower in mixed driving should drop the mpg about the same. The more you're into the boost the more that number will drop. When the car is not on boost, the differences in mpg versus a naturally aspirated automatic crossfire should be negligible. A tiny bit more weight -- a little bit of drag running the S/C belt (but the S/C clutch keeps that down to a minimum).