Conclusions
The tests show that Red Hat 6.1 and Debian 6.0.2 are mostly similar, if not identical, from a performance standpoint. While this was expected, as they have very similar software stacks (from the kernel to the various servers version), a practical demonstration is always welcomed!
However, there are two cases were the performances differences are sufficiently high to attract our attention: in Apache static web pages servicing and in PostgreSQL speed. In the former (static pages speed) the winner is Debian; so if you plan to implement an high load, mostly static web server, you will probably want to go for the Debian route. On the other hand, for a PostgreSQL database I would surely prefer a Red Hat system.
Note that I'm not saying that it is impossible to tune Red Hat to perform as Debian in Apache static test, nor that it is impossible to tune Debian to run as Red Hat in PostgreSQL: the point is that you had to tune them (eg: disable selinux) for accomplish this.
Please also remember that Debian ship with an installer that, by default, select an EXT3 filesystem without enabling write barriers. While this provide much higher performance with databases as PostgreSQL (up to 100%!) remember that in most cases this is unsafe. To safety turn off write barriers (in EXT3, EXT4, XFS and all others common Linux filesystems) you must disable any disk cache (a terrible thigh for performances) or use a battery backupped disk controller.
I hope that this information will be useful to you as they were for me.
Have a nice day!