While your reads weren't so bad, you couldn't disallow the chance that he did have a 9, especially if he had been stealing alot of pots recently. However, looking over the situation I feel that your read on his cards, either two overcards or a medium to low pocket pair, wasn't that bad a choice.
Looking exclusively from an odds standpoint, you were just getting the odds to move in here, given that you thought you had twelve outs. Furthermore, you said that he had been fairly loose recently, saying that he could have had a range of hands (a number which you could have beaten).
One of the things I think you are failing to realize is that you had an M of 20, and, in reality, where in no position to have to throw all of your money into the pot. Since it was immediately before the final table, I probably would have folded to fight another day, hoping to outplay my opponents at the final table. Yet, your argument regarding that you would be a massive chip leader is certaintly a part of this decision, I wouldn't have wanted to put my entire tournament on, possibly, a coin flip situation.