The producttabs query to fetch the best selling products parses 2M rows on our install. Because of that the widget takes 1 minute to load. Any suggestions on how to fix this?

Here the query:
https://gist.github.com/MichaelThessel/68e0bb6df8a12cd4ff2c

Layout XML

      <block type="producttabs/grid" name="new_styles">
        <action method="setParams"><params>class="mrb50"</params></action>
        <action method="setConfig">
          <name>
            <list_products_by>category</list_products_by>
            <title>New Styles</title>
            <product_category>4,6,5,7</product_category>
            <product_order_by>best_sales</product_order_by>
            <number_per_display>4</number_per_display>
          </name>
        </action>
      </block>