Selecting OS for High-availability/mission-critical web portal

Dear all,

I am a new system administrator for a company planning to create a web portal 
which provides email, IM, e-buisness, and search engine. Liferay is our 
portal management tool. 

I am searching for the best OS to be our platform. The required featuers are :

Attack resistance (I expect lot of attacks specially DoS).
Stability.
Performance.

Linux and OpenBSD are the main candidates for this mission.
Here I am listing my findings.


OpenBSD:
Pros 
^^^			
Security oriented on its base level (compilers, syscalls).
System over all stability.

Cons
^^^ 
Performance is not the first priority. Benchmarks shows clear performance 
degradation when compared to Linux 2.6.x.
Package management is not easy to handle like (e.g. apt-get and yum). 
User community/developers are quite small.
By using third-party packages (e.g. liferay, apache), system security falls 
back to those applications security level. (The system is secure as the 
weakest link in the chain).
The project has financial problems (e.g. 
http://www.linuxsecurity.com/content/view/122166/169/) which means that it 
might not survive.



Linux Debian with SELinux:
Pros
^^^
Apply mandatory access control (SELinux)
SELinux improves access control as whole, and immunity towards malware 
(proactive approach).
Larger community, more howtos. 
Stability.
Tons of ready made packages.
Very easy security patching system, supported by good security team.
Our main services (Apache MySQL, Tomcat, and Liferay) were tested mostly for 
Linux boxes.

Cons
^^^^
Performance degradation of 7% (SELinux) 
(http://www.crypt.gen.nz/selinux/faq.html#WWW.14).


My thoughts are that:

*OpenBSD will become vulnerable as much as the running service on top of it. 
Hence I will lose the legendary security it has.

*When I look at top 51 (http://uptime.netcraft.com/perf/reports/Hosters) Linux 
had 45% share. Which means that it is highly secure.

* With OpenBSD I am not going to spend time hardening it but rather trying to 
get the services (MySQL, Apache, ...) running on top of it. While in Linux 
installing the services is easy but I need to spend good time hardening the 
OS itself.

Any hint/comment is welcome.


 
Best regards,
Mohammad