The Subarches page lists all CPU-optimized versions of Funtoo Linux. Find the one that is appropriate for the type of CPU that your system has, and then click on its name in the first column (such as corei7, for example.) You will then go to a page dedicated to that subarch, and the available stage3's available for download will be listed. If you are using a virtualization technology to run Funtoo Linux, and your VM may migrate to different types of hardware, then it's recommended that you use a stage3 that is optimized for the oldest CPU instruction set that your VM will run on, or a generic image if it may run on both AMD and Intel processors.