I've gotten tired of mathematics slowing down the game (let's see... how many points above the difficulty is that?), so I've created a handy-dandy chart for checking whether various Attribute + Skill (+ Trait) + 2D6 vs. Difficulty combinations come out as Fantastic, Good, etc. The Difficulties go horizontally; the A+S(+T)+roll goes vertically. You'll notice I did 6-12 by 1's (because all of those numbers are commonly used, being A+S numbers--in fact, perhaps I should have gone lower), while above that, I skip-counted by 3's.