I was east and over 4♠ had bid 6♥. South passed my partner went into a mini tank and passed. North bid 6♠, I Xed, south passed and again a tank and pass. We took 4 tricks which was +500. 

My double of 6♠ was based on that I had to disregard my partner's tank and just pass on the info that I have ♠ loser(s).

7♠X would have been +800. But the point would they have sacrificed?