Is interesting that a quad core is required as arma struggles with using all of them. Reason is that arma wants them 2 cores all to itself and normal server processes get in the way.
HDD access is definitely a big cause of lag, reducing the logs and providing a dedicated and well optimised mysql server will go a long way.
I once experimented, some years back, with a quake 3 server. Based on Windows98 it did nothing beyond the required networking, loaded in dos, as the game engine took over everything else, we called it Q3OS and it ran like a dream and performed better than dedicated servers.. We used spares from our previous gaming pcs.
Maybe a stripped down server: ARMA2OAOS would work :) might need to put it behind a firewall though.
