I am currently running an 89 torque tune. I don't think my mileage got noticeably worse. I did notice a nice increase in power, particularly up to 3000 RPM or so. I also have a 93 torque tune but I haven't tried it yet...been pretty happy with the 89.
I thought about doing an e85 tune but there's only 1 station in my area and it's a 20 minute drive away, so not really worth it in my case.
There's a lot of other stuff you can use the tuner for...like compensating for tire size changes, differential gear changes, and transmission shift pressure.