Are we at the peak of the AI stock boom or merely in the foothills? To answer that question, a good place to start is with Ed Yardeni, an economist and astute US market commentator with a long track record of accurately calling markets. Overall, he's been arguing that we are only midway through a "roaring Twenties" for US stocks, generally powered by AI and surging productivity. That's prompted him to raise his projections for the S&P 500 continually.