1) Buy Intel. In servers, especially servers that take advantage of virtualization, having the extra performance is worth the increased cost.
2) Don't use Debian, unless you're building embedded appliances or something. Most open source packages are built against common server distributions (RHEL/CentOS, or Ubuntu server) - comparatively less are built for debian and other systems. If you end up venturing into commercial software - you're almost guaranteed to find that your vendor won't support anything other then RHEL (some won't even support CentOS, even though they're binary compatible)
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