First impressions:
I haven't had it out on the highway yet so I can't say what any improvments there are over 70km/h (~45mph).
Here goes, throttle response is smoother, revs up quicker (up through 4500rpm anyway). With the engine spinning freer shifting feels smoother as well. It also makes a great intake roar
Tomorrow I have my 170mi commute so I can let you know if there is any difference in performance and/or fuel mileage.