I know refurbs are getting slim in the Apple store. I want to find one before they are gone for good.
It may serve as a temporary computer as we slowly transition from a 2009 Mac Pro to a new Mac Pro setup for my wife's photography business. Don't want to spring on a new Mac Pro, new Monitor, and new Thunderbolt RAID drive all at the same time.
I'm kind of tempted by the server edition, but is it worth the extra cost? Can't you hook up two hard drives to the non-server edition? Which is the best value? I'm hearing everyone rave about the i7. Other than that, I don't know where to start.
For your purpose, get the 2012 i7 2.3GHz or 2.6GHz.
Base unit is enough.
Get the iFixit "Late 2012 Dual Hard Drive Kit"
Get a 3 TB harddisk
Get a 512 or 1TB SSD (Crucial or Samsung Pro)
Get 16 GB RAM.
Follow the various guides to remove the built-in drive and fit the hard disk and the SSD, create a Fusion-drive of the two.
Fit the RAM and you've got yourself a very nice machine that comes in not too far below the 4 core nMP:
http://browser.primatelabs.com/mac-benchmarks
in terms of raw CPU-performance.
GPU is a different story, of course. But it should not be such a huge problem unless you do video.
As your wife's business depends on it, I would invest in an external, FW-connected RAID-array for time-machine backups.
Not sure, how many of those are still available - the choice in pro-level external TB-arrays is much larger and of higher quality but you need the TB-port for the display, most likely.
So, it's either FW or USB3 (which you need to sacrifice an USB port for).
The MacPro doesn't have FW ports, so you would later need to sacrifice one TB-port for an adapter.
The Mini (2012 or 2014) doesn't do 4K, so you can watch from the sidelines while the various DisplayPort and HDMI-standards over 5K and 8K video mature and actual products come to market at reasonable prices.
The 2012 Mini was probably a bit to "open" for Apple's taste, so we got the more locked-down 2014 Mini last year ;-)
The only real advantage of the 2014 Mini (apart from its much faster PCIe-SSD) is its ability to drive two 2560x1600 displays (30 inch). The 2012 can only drive one of these and then a 1920x1200 via HDMI.
If your wife needs those extra 440x200 on the 2nd display, or you just need a 2nd TB2 port because you want/need to attach an external 8-disk enclosure, it's a tough decision ;-)