Why rushing to Debian?
Don't mistake me, I love Debian, I installed 1.0 and am still using it (not 1.0, Debian ;-), and I highly respect the security level they achieve.
However, as soon as the highest-grade security on an autonomous system is a concern, I personally consider that at least considering OpenBSD remains a must.
I fear to start yet another OS flamewar. Anyway I won't participate. I just mean that if I had to engineer such a box, I would consider bringing on it an OS that committed to security in the *first* place (whatever the motivation, name, genealogy or feature set).