SRT6 or N/A ?

I have an N/A, I see 22-24 around town, 29-32 cruising on Interstate at 65-70 MPH.
Lots of variables :
1. does the gasoline contain ethanol, is so, what % ( MPG drops 2-5 MPG with ethanol )
2. Temperature ( winter is better, denser air, no A/C running )
3. Tire pressure, the higher is is, the better the MPG. ( I run 33 rear / 32 front )