Nflight,
More to the point, what OS and engineering applications are you gonna run. That should more drive your purchase and direction for hardware, not the other way around.
Each OS has plenty of strengths and weaknesses. If you are hiring engineers to do heavy engineers type work, its already proven what OS they mostly prefer.( a hint?: in generally ends in (**IX) Are you going to run email, DNS, and web services, or modeling or simulation, rendering, Database software out of this setup?
Usually heavy engineering type applications are geared more for a particular OS where they are feature rich on a certain OS. The of course equates to where the spend the most development dollars, that will return them the largest profit for their software development investment.
I'm a Solaris bigot for Sun based hardware. I've run this for years on big sun hardware. I've also run plenty of MS, Novell, Citrix, etc. Do yourself a favor, run (**IX) on the servers, and a dual boot Windoze/Linux on the clients. That gives you all the toys on the desktop, and stability/security/adaptability reliability on the server.