Here's one way to do this in an attached workbook. There's a parameter for the Percent to filter on, and then a calculated field like the following:
IF [Pareto % of Total Sales] <= [Pareto Filter Param] THEN "Show" ELSE "Hide" END
Drag that to the Filter shelf and only select Show, and as you move the parameter slider different values will show up.
You started by saying that you were looking for this solution "...because the filter on the dashboard takes forever." Parameter-driven filters won't necessarily speed up a view all that much because they limit Tableau's ability to cache results, you might need to look into some other optimizations.
Thank ou Jonathan. You just made my day!