I really believe rune won't work like that, this is how I believe it will work.
Crit 6000
Mastery 3000
Haste 3000
>
Crit 6000
Mastery 6000
Haste 6000
-
It clearly says it takes the highest value of the 3 to determine the value of the other 2. Not combining then making that value the highest.