It's a rumor/myth that will not go away despite my many posts to the contrary.
To get SLI working in AH you need to go into Nvidia Control Panel under "Manage 3D Settings" and create a custom profile for AH. You do this by clicking the "Add" button (unless AH is already present in the list) on the "Program Settings tab and then browsing to the AcesHigh.exe to select it. Then modify the "SLI rendering mode" to use "Force alternate frame rendering 2" and SLI will activate for AH.
You can verify this by going to the Menu bar option under "3D Settings" and selecting "Show SLI visual indicator." This provides a HUD element that will be superimposed over the AH game, and you may then set your graphic options inside of AH to maximize SLI efficiency. The bar indicates SLI scaling and once you have the settings properly setup the SLI scaling should indicate somewhere near 95%. Even if the bar does not indicate much scaling you still have SLI active, so it is up to you to chose between a proper SLI scaling and FPS setting.
In the tower you will not get a proper scaling indication, so spawn out in the field somewhere to set your graphics options.
