here's my mpg report after installation. keep in mind this also includes a ~2in suspension lift, but still running stock tires.
highway: before i could get up to ~20mpg if i set cruise on 65mph. after i get 24-25mpg using cruise and 65mph. i've only done one test so far though, and it was after a few tanks of 91/93 octane (can't remember exactly which, some stores around here only have 91, some have 93).
city: i can't seem to get a good test yet, because there's somewhat of a design flaw. i can't keep my foot out of the accelerator because i keep wanting to hear that nice growl at about 3k rpm.
that being said, even with me being harder on it i'm getting 13-14mpg. before i would get ~12mpg if i was hot doggin a little more than usual.
other than that i can't -really- tell a difference in performance. it does -seem- (but could just be my mind thinking it is) slightly more responsive off the line or rolling 5-10mph. however after about 4500rpm it's just as wheezy and out of breath as it used to be.