I run Lubuntu Linux 15.04 on my box which is impressively lightweight and adds $0 to the cost of the box. It boots before the monitor can turn on and sitting at the desktop only uses 268MB of RAM. I do force the OS onto one core and Java onto the other so the MC instance gets its own 4.0GHz core and as it turns out that core has an amazing single core performance score. It really is a great cheap hardware setup for playing modded MC; not sure I could be any happier (for the benefit of anyone researching new hardware).