I've been playing with performance related settings more and found one
(a bit forgotten parameter) which made a big difference in my case.

I've set this in my web.xml

<context-param>
 <param-name>facelets.BUFFER_SIZE</param-name>
 <param-value>500000</param-value>
 </context-param>

Increasing facelets.BUFFER_SIZE to 500000 cut JSF response time almost in half!!!

This is for my case of rendering table see

http://www.jboss.com/index.html?module=bb&op=viewtopic&t=117092

As far as I understand this buffer is short lived (only during response) so
if there are not many concurrent request as same time increasing it
would not create any memory consumption problems.

Thanks,