It's not just the licensing fee for windows (100 additional bucks) but it's also the ability to have direct access to the hardware and to be able to completely control timing and priority. Linux was a pita sometimes (we fixed numerous driver and library bugs) but it really was the only option. We chose Ubuntu because it's the most user friendly and easiest to install. It is also pretty stable (this release anyway)
Does that mean you guys patched the scheduler to get the level of control timing and priority you required? Or was that not required in this instance?
We have been using Ubuntu for servers for a number of years now and have been happy with it.