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After checking how fast the standard 1TB disk is I will likely get a 120GB SSD, I have made very good experiences with my current setup, having apps and OS on the SSD.

If you already have a system that has its OS and apps on a SSD, you can skip this task.

My OS and apps are on a 160GB Intel G2 and my bootable clone (via CCC) is on a 1TB WD Black (the same which ships with the Mac Pro, although mine is the 64MB cache version). Every time I have to boot from the clone to restore something, I'm glad having paid the 400€ for the Intel drive. If you're used to a SSD, booting of a mechanical drive becomes just ridiculous. I really can't imagine working with a machine that doesn't boot from a SSD anymore.
No matter which type of mechanical drive you've got, the difference to a decent SSD is like day and night.

The Black drives are great for fast storage, though. Just a little bit too loud for my taste.
 
Thanks everyone for your input, I am writing this from my brand new Mac Pro 6-core, with 24GB of memory. What can I say, its awesome. Unbelievable.

Now I need to get more storage, the internal 1TB is a tad small, but I won't go for an SSD just yet (boot speed is fast enough for now).

I am thinking two 2TB internal drives... I am planning on doing a software RAID so that if one of the two 2TB internal fails, I can just replace it. Then I will get another external 2TB for offsite backup.

Is there a HD that you can recommend, or something I should stay away from? I found this and thought it would be suitable ($179):

Western Digital Caviar Black WD2001FASS 2TB 7200 RPM SATA 3.0Gb/s 3.5" Internal Hard Drive -Bare Drive
Cache: 64MB
Features: Dual processor - Twice the processing power to maximize performance
Parts: 5 years limited
Labor: 5 years limited
Model #: WD2001FASS
Item #: N82E16822136456​

Merry Christmas to all of you!
 
For what are you going to use those HDs? If it's just for storing files, then get Caviar Greens or other low-power drives. They are fast enough but more silent and cooler than Blacks
 
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