This is the setup that would get me out of my two year old C2Q running windows 7
When I first set up this system (an HP "elite" media center computer)
on Vista x64 I installed an intel 4gb Flash Cache "Turbo Memory"
and though "Flash Cache" was maligned by reviewers in it's notebook implementation it was highly effective in the 4gb user configuirable
Basically it was a 4gb SSD that functioned to turn whatever drive was being used as a system drive into a "Hybred" drive.
half of the 4gb was not user accessable and was used for start-up acceleration, the other half could be configuired for application launch acceleration and trust me it made Vista as fast (or faster) than I've ever seen windows7 move.
I still went Windows7 (pro x64) on this system because I have 7 on my primary notebook and metally switching gears between Vista and win7
AND with the purchase of my first "Advanced Format" hard drive the Flash Cache became useless, because the newer version of the intel matric storage manager required (it installs itself at startup) to run AF hard drives "kills" the flash cache driver
The new scheme for using a much larger SSD in a similar implementation
of Caching and acceleration is very attractive.
As for WD "Black" drives My system drive is a 120gb partition on a WD5002AALX 6.0gb/sec drive, I also have a pair of 750gb "Storage drives".
as for total ammount of space? after six months of operation my Windows 7 system with all my applications installed and system recovery set to 20%
has stabilized at 65Gb, that includes ~19gb of jpg images.
Storing Audio and Video data off the system drive is the best way to keep a system drive uncluttered.
I use an older e-mail program (Qualcomm's Eudora) which resides entirely in a seperate partition (e-mail programs that actually save the e-mail on your computer tend to be "dirty")