Thomas Knight ESC-350 supercharger and water injection

[zerodefects]

I have a Thomas Knight ESC-350 electric supercharger. This is the only real working electric supercharger that I know of. It is a centrifugal compressor hooked up to an 8hp electric motor (instead of the engine). One of the cool benefits of it is the ability to achieve its full boost (about 5 psi) instantly at any rpm. The disadvantage is that I can only run boost at WOT and only for a few 15 second spirts every hour (depending on batteries used and the alternator).
Since I won't be on boost all the time I'd like to run 87 octane fuel, then use the water/methonal when the supercharger turns on in order to prevent detonation with the added intake cooling benefit. This I think is an excellent use of water injection.
From what my research has found as long as I keep my water to 10% of my fuel (I am assuming mass, not volume) I shouldn't have any risk detonation problems at all. Also if I keep my water below 30% of my fuel I shouldn't run into any engine bogging problems. I know every engine is different but these are the guidelines that I used.
According to my calculations injecting 6 liters of water per hour will achieve these boundaries. I have a whole spreadsheet where I did the calculations (cfm, lbs of air, lbs of fuel, and water to fuel ratios), but what I am asking if this sounds *about right*. That does seem like a small amount to me. The car is a 3.8L V6 Mustang, redline is 5200rpms, boost is around 5psi (lower rpms a bit more, higher a bit less).
Thank you.