Still meaningless. You buy a Mac Pro for expansion and longevity. If you buy a MacMini as replacement you have some interesting cable management to enjoy. A MacMini is a macbook without a screen. They have limited memory allotments and relying on Thunderbolt for expansion gets expensive fast.
It totally will work as a lower end DAW. It is a very fast computer for what it is. But what it is is not a Mac Pro or even desktop replacement. No DSP via PCI kills it for anything higher level.
SSD's on SATAII vs. SATAIII really rely on your entire system being compliant to the speeds of the SSD. The fastest SSD's available have 4K r/w that is slower than a 1.5Gb link. How often do you use this type of r/w cycle? 85% of the time. If a SSD claims 550MB/s you only get that to another capable device. Streaming is different but a Mac Po can RAID0 4 WD Blacks and net 400MB/s+ internally on 8TB of data. Whisper quiet and no external case sleeping when you need it most. Like when your DAW crashes from waiting for a sample to spin up in your arrangement. If you feel your cash savings are worth the little details, that is cool and a personal preference. But it is not for everybody. I would gladly take a slower processor in a Mac Pro over any iMac or Macmini with consumer components. My preference.
I agree about the bandwidth limitations of Thunderbolt, both as a PCI-e replacement and as SAS alternative. This article proves it with almost a 3 x difference between SAS and Thunderbolt!
http://www.barefeats.com/tbolt01.html
But for audio work and as a boot drive, you've really misunderstood what makes an SSD absolutely smoke a hard drive, RAID or otherwise.
It's the massive amount of IOPs, 10,000s of them compared with all a drive can do which is move the heads around the platters at several MS making the random access time in the several hundred IOPs at most.
That's pathetic compared with an SSD and only useful for streaming low quantities of high bandwidth files.
That's exactly why hard drives score high in MB/s tests on large block sizes in the 1024Kbyte or more range but quickly drop off into single figures once they approach 4Kbyte sizes while SSDs just keep offering almost the entire bandwidth of your SATA interface at all times!
This is why they're such great boot drives and a dual drive system with an SSD to boot from and fast 7200rpm hard drive is the way to go.
I agree 100% about the longevity issue of a tower system but the cost issue is still the losing factor. My G4 has lasted me a long time simply because I've being able to upgrade the CPU and I/O etc... It's too long in the tooth now to be of any use as more than a server and a noisy one at that.
A Mac Mini has far more uses as a second system in the home too because of it's size and low power consumption.
For example I "Could":-
Get a used 2007 Mac Mini for about £250 on eBay and use it as a tie over system while I save up for a i5 based Mac Mini.
Make do with a Firewire 400 external case. One with the appropriate Oxford Semiconductor chipset can be had for under £40.
Buy a Core i5 based Mac Mini. Use Migration Assistant from the Core 2 Duo model to move my Pro Tools LE installation to the i5 system.
(The ONLY way of running it under Lion and it's not even supported, it just works for now and AVID want BIG money for a crossgrade if you want to run any new version of Pro Tools on a Mac running anything higher than Snow Leopard, which is their entire range).
Buy the lower-flex cable, a Vertex 3 and a USB 2.0 universal drive adapter.
Clone the i5 Mac Mini's drive to the Vertex 3 replacing the i5s internal drive with it and fitting my existing SSD in the lower bay with the flex cable to use as my recording drive, completely eliminating the external recording drive issue entirely and then use the Firewire drive for my iTunes library and general storage!
Then I'd just need to...
Use the older Mac Mini model through an LCD TV as a media centre with the addition of a Crystal HD Mini-PCIe card for use with XMBC and buy the Pro Tools crossgrade last, getting myself a nice little media centre into the bargain and a brand new Mac with a good few years use.
Or....
I could look for a used Mac Pro in the price range of the entire setup, notice how much value they lose over time and pick up a 2.8Ghz system with roughly the same CPU power as the 2.3Ghz Core i5 Mac Mini for around £1,100 used.
That would take me close to a year to save up for, I'd forfeit the whole media centre idea altogether because using my old G4 is out of the question because it's just too slow and far too noisy to be on 24/7 and I'd still have to shell out for the Pro Tools cross-grade eventually on top.