You really answered your own question
Alky injection will not give a definitive octane number due to the added benefit of its cooling properties. The closest you can come to getting a real number is to see what you can run with Alky and then try to duplicate it with only a certain octane fuel.
I would definately agree that Alky injection is better than 100 octane. There are numerous people who have run about the same numbers (give or take a little) with Alky as with 110 octane, and slightly slower than running C16 (116 octane?) so your saying 108-110 octane would be a pretty good assumption.
Also alot of people running 108 or 110 octane chips with Alky with no problems.