Which potential is better? 21% att or 75% boss?

Hey guys,

I used a black cube on my 21%att 12%dex fafnir dagger, and the new lines are 75% boss and 9% crit.

Which one is better to keep?

I think %attack is better if you already have over 200%boss

Maybe you can use example in here to calculate.

#4 http://www.southperry.net/showthread.php...0additive?