Only one station in town has 93+ and that is Chevron. All the others the best is 91. Any issue do you think with 91? (normal city driving of course) 93+ for stomp and steer w'end drives....
Running 100 octane will make your car less powerful...? lol - these cars are developed to run a minimum of 91 from the factory, but it will make more on 100 octane, not less... Most ECU's are designed to pull and add timing based on dynamic advance tables that are enabled based on certain criteria, air intake temps, knock, exhaust has temps, etc... The bases of your post is technically correct given all things equal, but not applicable in a boosted car with modern ECU capabilities... Running higher octane fuel than the minimum required 91 will place your ECU in the happy zone and allow it to run full programmed timing = more power and for longer because of the added cooling effect of the higher, slower burning fuel...
Also, higher octane fuel isn't made by just adding water, haha. Go ahead and try that on your car and let us know how it works out for you... There's a reason why fuel companies use octane boosters with nitrogen carriers. Most use methanol, isopropyl alcohol, naptha, xylene, toluene), benzine, hexane, nitro benzine, aniline, etc., but they never tell you exactly what or how much they use - its called trade secrets... Those additives they add to the fuel do a lot to combat all of the negative effects of running unleaded fuel, such as varnish and deposit build up, storage life, reaction to oil, etc... These aren't issues with leaded fuel but are with unleaded...
Granted, you will make much more power by tuning your car to optimize the timing for the higher octane... But there is no way you'll make less HP - the statement is true if you run lower octane as the ECU will pull timing and will run much hotter....