Interesting system, I like the simplicity but I am not sure about the exponential increase, I would have to think on it further. Harnmaster also has an interesting and simple system for special success that is linear: every roll where the digit is either "0" or "5" is a special result. So overall there are 20% of 'specials', and the fraction of those specials that are special success as opposed to special failures is your skill. If your skill is 50, half of the specials will be special success, the other half special failures. If you skill is 80, then you have 16% chance of a special success and 4% chance of a special failure. I always thought it's a great way to manage that (no math or table involved), but (like Revolution) it doesn't include a 3rd level of success.