Great job, but I'm not sure, who ever did this, that it's correct.
If you read this: "Almost all weapons and armor can be safely enchanted to +3, but beyond that, success is based on a pre-defined rate of probability." Copied and pasted from
If you read it carefully "but beyond that, success is based on a pre-defined rate of probability", so it's not 67% after being at +3.
Before they have updated their site it said "but beyond that it has a 1/3 chance of breaking or "failing" ". I have always understood it.. so it has 66.6666... chance of success.
But now I'm not sure. So I don't think it's accurate.