the 70-200 2.8 is superb on it's own, but when i've used the Sony 2x i found there's too much hunting in the focus .. i tried them together at an airshow and won't be doing it again, lost too many shots.
there will be some times it would be ok if you can put up with a slight drop in IQ, but i'd rather use the 70-200 on it's own, or the 70-300 G/70-400 G