By Anne Holland, PresidentAs I reported in a recent column, 3,637 Marketers Reveal Which Email Tests Worked Best, MarketingSherpa research into 3,637 real-life marketers' tests showed landing page copy tests were the big ROI winner.On the one hand, this didn't surprise us because landing page tests have ranked as the highest impact tests in other online media for years. In fact, a December 2006 MarketingSherpa study of the world's heaviest online advertisers revealed that 56% had budgeted significantly for landing page A/B tests in 2007. However, let's face it -- when you think about email tests, traditionally you think about stuff like subject lines, copy and offer, and text versus HTML. It's not that the old tests don't work --...