We use our old 5,1 12 core as a server mac now. It became too frustrating working with FCPX in an older hardware system because they’re just designed for an older generation of software. Now that it has just one job to perform of managing a 10gb ethernet server and 2 60TB arrays, it’s great.
With all due respect, it seems like your preconceived notions about iMacs, laptops and “dustbins” are clouding your understanding of what these systems are actually capable of nowadays. The type of RAM you can put in these systems just isn’t as fast as the RAM you can put in a new mac system of any flavor. In fact, I think I once priced out a RAM upgrade on the 3,1 and it was so overpriced (because it’s no longer in production perhaps) it wasn’t worth the effort.
There are other really important things you might be overlooking. Thunderbolt 2 is no joke. USB3 is also a game changer. Connected to something like a RAID5 Areca 32TB Thunderbolt Array, these systems all beat the pants off of an internal 4 drive array in RAID 0 (in 3,1 as well as 5,1) that isn’t even capable of taking advantage of 6G drive speeds. Lastly, the internal SSD’s on new macs really do rock.
Life moves pretty fast Neil. If you don’t stop by your local apple store to smell the upgrades, it might pass you by :).
You can compare any model of mac to another here:
https://www.everymac.com/ultimate-mac-comparison-chart/?compare=all-macs
I made the comparison for you here.

For what it’s worth, I decided to reduce our home system from an office to just a desk last year to make space in the home. I now have a retina MBPro 15″ feeding to a tastefully hidden Promise Pegasus 8Tb array which is ample. When I want to view something on a big screen, the new mac systems are capable airplay to the apple TV 60in screen in the same room. Older systems can’t do that. If I want to see something in 4K, I run the HDMI out of the iMac into the TV. It’s a simple, beautiful and surprisingly robust system – that will get out of the way if I ever need to use the desk for something like changing a diaper :).
John Davidson | President / Creative Director | Magic Feather Inc.