You quite probably won't get decent x86 emulation speed out of an ARM processor. It takes an order of magnitude more transistors than an ARM has just to make an x86 out of hardware. You can do code translation on the fly, but doing that and keeping your virtual environment anything like the server you are trying to emulate.
When it comes to simulating servers, I've been opting for things like lxc and openvz. OSX should be able to use BSD's jail.
VirtualBox has been a boon for me for virtual server environment testing.