Re: Lateral approach
> There is no loft and there is no space in the cupboard.
Virtualization is no silver bullet. It doesn't matter what tech you are using. This applies even to high end Unix server systems. If you have high performance and responsiveness requirements, decoupling two competiing operating systems is a better way to go. There are plenty of viable options here. The Intel NUC has been all over the "blogosphere" lately. There's also the Brix. That has plenty of power.
It's pretty easy to have a "CPU-in-can" setup similar to the new Mac Pro. Just put a suitable CPU on a mITX board and put it in as small of an enclosure as you want. If you don't care about the GPU in a Linux box you can make a LOT of compromises.
I would tend to avoid virtualization for anything compute heavy or IO heavy that's bound to come in contention with other VMs or the host OS.