On my 3rd tank of E30 mix I got 22.47 MPG. So I ran 3 tanks of the E30 mix and my average MPG is 21.29 MPG, which is not bad at all. I was averaging 21-23 MPG on my 93 tune, so relative to that, 21.29 MPG with E30 is pretty good in my case.
As a tip to newbies who might want to try E85 and are worried about tracking their mixes. You can use Fuelly to track your fill-ups and add notes regarding your ethanol mixes. You can use an ethanol calculator to estimate the current ethanol content in your car, then note that down along with how many gallons of E, in the notes section for your fill-up in Fuelly. Doing it this way, I am able to calculate what my estimated ethanol content is for the latest fill-up, by looking up what the estimated ethanol content was on my last fill-up.