Which Linux/Linux distros may the best for building a reliable and secure server

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http://www.linuxquestions.org – Dear all ! As per my gr8 interest in open source system,I have chosen a project "design and development of a secure and reliable open source HMI/SCADA system." My HMI system have to communicate and cater data of a plant where 100s of processes will be running simultaneously. I am not very sure which Linux distros will best meet my need. I am not interested in SELinux. I want to use PostgreSQL. I will be more happy if your answer will include related support/support link for suggested Linux/Linux distros to give good startup to this project. Will it be a good idea to choose centOS ? (HowTos)