I have been using Tesco 99RON for a few months now as the petrol station on my way into work sells it for 98.6p a litre - actually I think it's gone down a penny recently. Before that I always used 97 or 98RON such as: Esso Super / BP Ultimate / Optimax - erm - I mean V-power. I haven't used 95RON for years!
Anyway, first thing I noticed was that my standard 172 seemed to pull better low down (between 2-4k) and removed a very slight flat-spot around 3k. I just chailked that up to me thinking too positively about the new fuel, but it seems to concur with what has been said on here.
Second noticable thing is the MPG. With 97RON I got about 32-33mpg and with my right-foot being susceptible to gravity, I didn't think that was too bad. Now with 99RON I really have to cane it to get below 35mpg. On steady, long motorway runs I bet it pushes 40mpg.
Overall, i am really impressed with the fuel. Would certainly recommend using it for a few tankfulls!
Still looking for a place that does BP102 though!