Im seeing about 2mpg difference. Maybe less. Its still a bit early to tell @ 1500 miles.
My experience with the last and current Sube is that I do better around town tuan on the interstate.
Where I live is slightly rural with mostly 40-50mph zones, so I get phenomenal mileage.
At 70 with the cruise on and the ac, on flat ground, my xv or former impreza barely do 30mpg.
55 is where the mpg's really drop.
The gearing on the xv feels a good bit better than the impreza, and around town it feels less bogged down.