Ok I don't have an 8, but I will share my experience with my XR6. I got the Unichip done on my XR6 3 weeks ago. I had it tuned on
Standard Premium Unleaded and not Optimax, because I don't always have access to a Shell station when driving. According to Croydon Auto Sports Dyno, Peak Power increased from 124Kw at the back wheels to 132kw ( a jump of 8kw)(The car has a full Herrod Motorsport Exhaust and Crow cam) However, this doesn't tell the full story...at the low end and top end the power difference was as high as 15kw at the back wheels..which is very noticeable under kick down acceleration conditions. However, better than this is the fact that I now get around 35Km more per tank.
ps: Its interesting to note that C&Vs dyno recorded my car as having 129Kw at the back wheels prior to the Unichip, whilst Croydon Auto Sports recorded 124Kw at the back wheels prior to the unichip. Both dyno curves were however the same in shape...Hmmm