In any other metagame Eviolite wouldn't make any difference for the Chansey/Blissey debate since Blissey took no Special damage regardless, and 50% more defense doesn't make too much difference on 5 base and less HP, whereas 55 base Sp. Atk would. But I guess B/W is past the point of the infinite special wall now... And Seismic Toss doesn't care about Sp. Atk either, too, I guess.