Tolerance is complex issue. While there are people whom have functioned near normal at extremely high BACs, tolerance is not complete protection from the effects of heavy use. Take liver disease for example. Very few heavy drinkers will suggest that they are immune to this due to their heavy drinking. For almost all of us, having a BAC > 5 means you no longer need to worry about liver disease. You won't need a liver.
> .4 BAC death likely
> .5 BAC death very likely