You'd need to compare tank to tank really..I don't think my Vectra c 1.8 120 likes it much. Seems to loose 4-5 mpg. I use the Supermarket 99 and get 48 mpg at 70 mph.
I wouldn't put e10 in anything remotely performance, especially forced induction..Maybe coincidence, but I had to whack some E10 in to the Subaru, and it went in to limp-mode almost straight away. In 5th gear it usually makes about 19 lbs of boost. Making the safe 6 lbs at the moment. I put some Esso 99 in the other day, and it's OCCASIONALLY boosting properly.