This post is about best partitioning scheme and doesn't consider (yet) different filesystems or format options, nor (yet) which distro to install. The configuration is under scrutiny is NOT for gaming or for simple desktop usage, but for HTPC and HDMI usage.

Hallo all, I have a spare motherboard around and I want to build a media center based on free software and licensed codecs, GNU/Linux distributions and one or more iterations of what have been done for the living room linux enjoyment.
My questions revolve around the need to optimize the resources without adding expenses, and I want to ask you suggestions about the partitioning scheme first.
Details: the mobo is a P5ADZ-E Premium, equipped with Pentium IV 631, 4 Gb of RAM on two sticks and it will sport a GF 9600 with 1 Gb of memory; the PSU is either a 540 or 630 Watt item. Audio, USB, Firewire, Gigabit, SATA and PATA, all is on-board with no expansion (maybe a DVB card could be included on either the PCI or PCI-e bus). You can see the specs to make up your metrics.

I have the following disk at hand now:
- 2 Samsung HD753LJ/750 and 1 HD103UJ/1000
- 1 ST3500320AS 500
- 1 Raptor WD1500ADFD/150
- 2 cheap SATA150 disks for 40Gb sucked up somewhere
- 2 PATA ST400832A/400.

Now, if you readers are cognoscenti, imagine the workload of a heavy AV configuration: the huge screen on which I assume huge things get going, streamed or not but surely 1080p, and the torrents running, the internet radio too, a DVD playing on the LAN, if possible someone connected from another room to the mobo's 802.11g should be able to play music or videos. Yes, that Flash thing as well... Additionally, a disk could be plugged for Redmondism, therefore Virtualbox or VMware or Wine should be called in to resurface needed content from a Microsoft past.
The motherboards was never used, the CPU was. The 755 socket gives me the choice of a dual Celeron but I preferred to go HyperThreading instead to retain the whole shebang of that ISA instructions. No RAID is intended because a 3 Ghz processor with HT is supposed to do most of the above in 4 Gb of RAM using onboard SATA, LVM is preferred instead to consolidate the space on the big Samsungs, and to create other volumes where needed.

What is the best disks' usage for a low-latency oriented partitioning scheme?
In my intention the Raptor is the disk where very fast thing have to happen, like transcoding and AV heavy stuff ( about which I know very little). The small SATA150 might be deployed for the only goal of creating a DMZ in case of big LAN, or any Internet paranoid settings: the PATA is big, fast, handy enough for any deployment.
So I need to set root & family in the smartest way, and my options are laid down like this:

/boot / PATA 400Gb
swap /home SATA 750/1000Gb
/tmp SATA 750Gb
/opt SATA150 150Gb Raptor
/DMZ SATA150 40Gb

or:

/boot / /home SATA 1Tb
/usr SATA 750Gb
swap /var SATA 750Gb
/Raptor SATA150 150Gb
/DMZ SATA150 40Gb

or just:

/boot /everything SATA 1Tb
/everything SATA 750Gb
/everything SATA 750Gb
swap /tmp PATA 400Gb
/Raptor SATA150 150Gb

This configuration is expected to do at least 3/4 things at a time reading on all disks and delivering data to more than one location. If you check the specs of the mentioned components you can have an idea of what these not-so-recent disk are able to do in terms of density and cache and rotation and so on: does it still matter, with such big Samsung, to separate / and /usr, or /home? Does separating /tmp, /usr or /opt benefit multitasking and ripping and playing?
Alternatively, do you think that my worry is just theoretical (in fact, I still haven't installed anything) and the motherboard, the GPU and the CPU do have enough juice to stand and deliver audio, video, torrents and DVB without messing with head contention, bus contention, sequential reads or else?
Thanks for the help, ask for more details if needed.

Ennio