IIRC you could run ESXi 4.1 on the top system - it's Core, not Core 2, based, so it's a bit 32 bit crippled, but it would still work....stick 16gb in there and you'd have a simple basic system.
But a NUC would likely be about as fast and far smaller and easier.
But a NUC would likely be about as fast and far smaller and easier.